Official information
Officially called Dragonborn.
Released for xBox 360 on December 4th 2012 for 1600 Microsoft Points. No announcement has been made for PC or PS3 versions, nor has there been any mention of exclusivity either way.
It is marketed as a game Add-On, like Dawnguard and Hearthfire. Take what you will from that....

Teaser picture http://cdnstatic.gamesas.com/bethblog.com/wp-content/uploads/2012/11/681455957.jpeg.
Video http://www.youtube.com/watch?v=TRmdXDH9b1s.

Observations
Video contains information about some ex-Dragon-Priest-come-hipster-Dragonborn who ruled over Solstheim and liked to eat dragons. He makes a return in Dragonborn.

Links to interesting parts of the video and their respective stills.
(give me more links and I'll put them here, append #t=XXmYYs to the video URL for timecode)

Albums containing the same + more stills.
http://imgur.com/a/8ezW3
http://imgur.com/a/l4yL2 (Can you identify some of these?)

Every frame from the trailer http://www.mediafire.com/?ymyt9gap5k2w1xi


Speculation
Boat Arrival into what is likely where Raven Rock was.
Antagonist is a former Dragon Priest, as well as the first Dragonborn and had dominion over Solstheim
Redoran Architecture present in walled city.
Giant Mushroom foilage. Terraformed Solstheim or Nothern coast of Morrowind?
Several new Daedra - One of which looks eerily like the Sixth House priests in service to Dagoth Ur

Info found in 1.8 CK update
Player dragon mounts are in.
2 new Achievements out of, at least, 10 are Solstheim Explorer, of which you need to discover 30 locations, and Stalhrim Crafter

Info found in 1.8 Updates
The next DLC will be called Dragonborn and it will be set on the island of http://www.uesp.net/wiki/Lore:Solstheim.
The main locations you will be able to visit are http://www.uesp.net/wiki/Bloodmoon:Raven_Rock, Miraak Temple, http://www.uesp.net/wiki/Bloodmoon:Castle_Karstaag and a Telvanni tower (N.B.: Not the Telvanni Tower seen in Morrowind in Vivec, but http://www.uesp.net/wiki/Morrowind:Tel_Uvirith).
There will be some new armor types, http://www.uesp.net/wiki/Morrowind:Bonemold, http://www.uesp.net/wiki/Morrowind:Chitin, http://www.uesp.net/wiki/Morrowind:Nordic and http://www.uesp.net/wiki/Bloodmoon:Raw_Stalhrim each having heavy and light classifications.
Out of these new materials, you will be able to craft new types items out of two of them, namely Stalhrim and Nordic.
http://www.uesp.net/wiki/Morrowind:Spears will be added along with an array of new creatures/automotons, http://www.uesp.net/wiki/Lore:Riekling#Riekling, http://www.uesp.net/wiki/Lore:Scrib#Scrib, http://www.uesp.net/wiki/Morrowind:Netch#Netch, http://www.uesp.net/wiki/Lore:Boar#Boar, Benthic Lurker, Ballista Centurion, and something with an internal name of HMDaedra, quite possibly referring to http://www.uesp.net/wiki/Lore:Hermaeus_Mora since it lists his plane of oblivion, Apocrypha. You will also be able to ride dragons and be in combat while mounted on one.

http://i.imgur.com/gF1hJ.png is what the quest header for Dragonborn Quests will look like, and http://i.imgur.com/AJu91.png is what the compass markers look like for the new locations.
From the top, clockwise: Telvanni Tower, To Solstheim, Raven Rock, Castle Karstaag, Standing Stones, To Skyrim, Miraak Temple.

There will be at least two new tracked stats: Dragonborn Quests Completed, and Stalhrim Items Crafted

You will travel to Solstheim via a boat, much like you did in Bloodmoon, although this time, it looks like you may at least get a partial visual boat ride.
The Telvanni tower has float up and down animations, so no levitation it seems.
Dragon riding will take place in its own world space

Mounted combat looks like it's getting an improvement with the ability to cast spells while mounted, tihs isn't necessarily a Dragonborn only thing though!

It appears that Update 1.8 readies Skyrim for PS3 DLC.

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Misinformation:
Weapon degrading -- There's nothing to indicate this is added, that isn't to say it can't/won't be added however. There was just no "new" information in this update. The degradation stuff seen previously has all been renemants from previous CK games (Fallout)
H2H stuff, That was my diff program messing up, sorry
Release dates -- No one but Bethesda knows!

Other stuff that I can't put my finger on or give intelligent guesses about because of lack of information
Miraak death animation, Chieftain animations, Chisel animations (perhaps new crafting station for the new armor.. doubt it though), Storn Death Reaction animation & Storn Suit Stages, Frea, Pray, StonePickUp, KillMoveDLC02RipHeartOut, TreeAmbush
There also seem to be a lot more animation files for running with weapons. No idea why.
Dwarven Ballista -- Possibly a new trap? http://www.uesp.net/wiki/Skyrim:Dwemer_Ballista#Dwemer_Ballista

Previous Threads
http://www.gamesas.com/topic/1417057-time-for-some-spoilers-form-the-latest-beta/, http://www.gamesas.com/topic/1417092-hints-found-about-the-next-dlc-found-in-18-beta/, http://www.gamesas.com/topic/1417136-18-beta-update-and-dragonborn-dlc-hints-discussion/, http://www.gamesas.com/topic/1417175-18-beta-update-solsthiem-dlc-hints/, http://www.gamesas.com/topic/1417237-18-beta-update-solsthiem-dlc-hintsagain/, http://www.gamesas.com/topic/1417280-18-beta-update-solsthiem-dlc-hints/, http://www.gamesas.com/topic/1417375-18-beta-update-new-dlc-discussion/, http://www.gamesas.com/topic/1417315-18-beta-update-solsthiem-dlc-hints/, http://www.gamesas.com/topic/1417392-18-beta-update-solsthiem-dlc-hints-thread-9/, http://www.gamesas.com/topic/1417456-18-beta-update-solsthiem-dlc-hints-thread-10/, http://www.gamesas.com/topic/1417500-18-beta-update-solstheim-dlc-hints-thread-11/, http://www.gamesas.com/topic/1417552-18-beta-update-solstheim-dlc-hints-thread-12/, http://www.gamesas.com/topic/1417570-18-beta-update-solstheim-dlc-hints-thread-13/, http://www.gamesas.com/topic/1417620-18-beta-update-solstheim-dlc-hints-thread-14/, http://www.gamesas.com/topic/1417703-18-beta-update-solstheim-dlc-hints-thread-15/, http://www.gamesas.com/topic/1417802-18-beta-update-solsheim-dlc-thread-16/, http://www.gamesas.com/topic/1417929-18-beta-update-solsheim-dlc-thread-17/, http://www.gamesas.com/topic/1418010-18-beta-update-solsheim-dlc-thread-18/, http://www.gamesas.com/topic/1418096-18-beta-update-solstheim-dlc-thread-19/, http://www.gamesas.com/topic/1418331-18-betasolstheim-dlc-discussion-thread-20/, http://www.gamesas.com/topic/1418474-18-betasolstheim-dlc-discussion-thread-21/, http://www.gamesas.com/topic/1418670-18-betasolstheim-dlc-discussion-thread-22/, http://www.gamesas.com/topic/1418874-18-betasolstheim-dlc-discussion-thread-23/, http://www.gamesas.com/topic/1419074-18-betasolstheim-dlc-discussion-thread-24/, http://www.gamesas.com/topic/1419436-18-betasolstheim-dlc-discussion-thread-25/, http://www.gamesas.com/topic/1419724-18-betasolstheim-dlc-discussion-thread-26/, http://www.gamesas.com/topic/1419844-18-betasolstheim-dlc-discussion-thread-27, http://www.gamesas.com/topic/1420204-18-betasolstheim-dlc-discussion-thread-28, http://www.gamesas.com/topic/1420420-18-updatesolstheim-dlc-discussion-thread-29/, http://www.gamesas.com/topic/1420627-18-updatesolstheim-dlc-discussion-thread-30/, http://www.gamesas.com/topic/1420666-18-updatesolstheim-dlc-discussion-thread-31/, http://www.gamesas.com/topic/1420699-18-updatesolstheim-dlc-discussion-thread-32/, http://www.gamesas.com/topic/1420797-18-updatesolstheim-dlc-discussion-thread-33/, http://www.gamesas.com/topic/1420887-18-updatesolstheim-dlc-discussion-thread-34/, http://www.gamesas.com/topic/1420987-18-updatesolstheim-dlc-discussion-thread-35/, http://www.gamesas.com/topic/1421043-18-updatesolstheim-dlc-discussion-thread-36/, http://www.gamesas.com/topic/1421094-18-updatesolstheim-dlc-discussion-thread-37/, http://www.gamesas.com/topic/1421130-18-updatesolstheim-dlc-discussion-thread-38/, http://www.gamesas.com/topic/1421151-18-updatesolstheim-dlc-discussion-thread-39/, http://www.gamesas.com/topic/1421157-18-updatesolstheim-dlc-discussion-thread-40/, http://www.gamesas.com/topic/1421165-18-updatedragonborn-dlc-discussion-thread-41/, http://www.gamesas.com/topic/1421172-18-updatedragonborn-dlc-discussion-thread-42/, http://www.gamesas.com/topic/1421192-18-updatedragonborn-dlc-discussion-thread-43/, http://www.gamesas.com/topic/1421221-18-updatedragonborn-dlc-discussion-thread-44/, http://www.gamesas.com/topic/1421272-18-updatedragonborn-dlc-discussion-thread-45/, http://www.gamesas.com/topic/1421326-18-updatedragonborn-dlc-discussion-thread-46/, http://www.gamesas.com/topic/1421437-18-updatedragonborn-dlc-discussion-thread-47/

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All of the above is speculation over new strings found in the files from the 1.8 update, and should not be treated as facts or as any proof that any of it will even make it into the game! (but you all already knew that, didn't you!... Didn't you?) They were found by comparing 1.7.7.0 files with those in 1.8.145.0. The update to the Beta (i.e. 1.8.151.0) gave no new information.

You want proof, look at http://www.gamesas.com/topic/1417392-18-beta-update-solsthiem-dlc-hints-thread-9/page__view__findpost__p__21660925 http://www.gamesas.com/topic/1417392-18-beta-update-solsthiem-dlc-hints-thread-9/page__view__findpost__p__21660876 http://www.gamesas.com/topic/1417175-18-beta-update-solsthiem-dlc-hints/page__view__findpost__p__21656816 http://www.gamesas.com/topic/1417057-time-for-some-spoilers-form-the-latest-beta/page__view__findpost__p__21653361, and http://www.gamesas.com/topic/1417092-hints-found-about-the-next-dlc-found-in-18-beta/page__view__findpost__p__21654653 for dragon riding. Also, http://www.gamesas.com/topic/1421192-18-updatedragonborn-dlc-discussion-thread-43/page__view__findpost__p__21749310 for the CK Update.

Also you can look through (my) Mardoxx' previous posts http://www.gamesas.com/index.php?app=core&module=search&do=search&andor_type=and&sid=dc5763cc2fa8668a67e4ba28567b4374&search_author=Mardoxx&search_app_filters%5Bforums%5D%5BsortKey%5D=date&search_content=both&search_app_filters%5Bforums%5D%5Bforums%5D%5B%5D=118&search_app_filters%5Bforums%5D%5BnoPreview%5D=0&search_app_filters%5Bforums%5D%5BpCount%5D=&search_app_filters%5Bforums%5D%5BpViews%5D=&search_app_filters%5Bforums%5D%5BsortKey%5D=date&search_app_filters%5Bforums%5D%5BsortDir%5D=0&search_term=&search_app=forums&st=0

For official announcements, check http://www.bethblog.com/category/skyrim and the official forums here.

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i started playing morrowind goty i hope thefighters guild returns sent from my xbox using ie

I really hope Bethesda comments on the DLC confusion. It's frustrating to be on PS3.

They basically ignored you for months. Why stop now? Never change a running system.

pc 2

i think ps3 still has 2 wait

I still think Bethesda will make it up for the PS3 users some-day... Maybe.

So there looks like bull netch and maybe a betty in there too. scribs are in as well, but i have not seen one in the trailer. so, i think its a smart bet that there is going to be some dunmer agriculture because those creatures produced things that were important to the dunmer economy.
will the east empire company have any involvement? this is solstheim.... they have a foothold or two, though they apparently left the ebony mines they could still be trading with whats left of these great houses.

If im not mistaken, before the release didnt they say that the companions were supposed to be "the fighters guild" in skyrim when questioned why they werent returning...?

Well some-day isn't soon enough for me. I'm getting a new video card and Skyrim for the PC on Friday. Also, am I just slow or has anyone else notice that at the ends of the quest header it looks like a squid guys silhouette?

Correct. I was excited to see the Companions prior to release, then I joined them and I've never been more disappointed with something in a TES game.

For as much as I dislike Oblivion, the Fighter's Guild was so much better than the faction we got masquerading as the companions.

It was interesting, wasnt it?

After completing the companions it made me wonder why there couldnt be the companions and the fighters guild?

Considering it seems like the 2 factions are so philosophically different... Hm, oh well...

This place looks a little "empty". I hope it is only a work-in-progress picture.

Messy how?

It looks to me with too few environmental features: plants, rocks, this kind of things.

I do kind of agree with this, but I personally like the DB and TG the most in Skyrim.

On a side note, I wonder how many faction questlines will be in Dragonborn.. or if it will just be a choice between two like Dawnguard.

that seems to be a problem with the island in general, does not seem that visually distinct from the rest of skyrim, i agree though the telvanni area looks really barren... BUT that could possibly not be on solstheim at all though, it might be small volcanic islands formed after the red year that are nearby that we can travel to. if so then this "dlc" will be big enough to be called "expansion" by my standards.
i was actually surprised at how large dawnguard was, i expected it to be smaller. THIS looks massive though. the island itself is not very big, but it seems that its not just the island, we have the Apocrypha which may be as large as soul cairn or larger. and IF we have telvanni islands that is sufficiently large enough for me.