Take things slow and/or follow certain rules. Some people also grow attached to their character and want to see how it develops, though I find this hard to udnerstand. But hey, who am I to judge?

600+ hours, and done most things...and I say most because with my second character I've already discovered places and things my first didn't.

It's fairly easy:

Limited fast travel;
Use caution a lot...meaning sneaking, particularly in dungeons;
Do a lot of radiant and side quests;
When you go to a town or city, visit all the shops and local celebrities, and talk to everyone and just loiter around to pick up the gossip;
Explore a lot, including going places just to look at the view;
Spend time alchemising, smithing, trading or simply tooling around in your booty chests;
Go visit places just because it's a good day and you'd like to go there;
Wander around hoping to attract some dragons for a fight;
Go Thalmor hunting.

Just realized, 100+ hours in game and I have not completed the main quest.

I only have one character and I've played 265 hours with him, with many more hours to come.
He's level 55 and the leveling has almost stopped, since I still use the same skills that I've all but maxed out already.

According to the stats, I've found 264 locations and cleared 83 dungeons. I've played 11 main quests and 10 sidequests, as well as played through the Thieves Guild.
Now, how come I've only cleared half the amounts of dungeons as you have and yet am on the way to 300 hours?

Well, first I am a stealthy guy who always sneaks in dungeons, except when they're cleared. I also pick them completely clean, wouldn't want to miss a single mushroom or ancient nordic plate for my collection. A 2-level dungeon can often take an hour for me to clear.

Then I haven't used fast travel for the last 100 hours, and used it sparingly before that as well. I use carriage now and then, though.
I've also spent at least 30 hours decorating my home in Solitude. And probably 10 hours of reading books. And several hours pondering on the Perk selection screen.

And even though I'm rich since long ago, I still collect loot and sell it off, trying to reach a million Septims (Medes?). When returning home, it often takes an hour for me to just organize the loot I want to store in my house, and sell the stuff I want to sell.
I consider myself to be a light roleplayer - I only eat, sleep and dress accordingly when I feel like it or when I remember it.

Running from point A to point B also takes time, since I usually collect every ingredient, mine every ore and kill every animal I see along the way. And of course the journeys are often as much exploration as travel, with me running around trying to climb mountains, searching through every nook and cranny and marveling at the beautiful landscape (screenshots and new desktop wallpapers!).

It all has to do with playstyle. If you run straight from point A to point B and only do what it necessary to complete the quests, as well as playing a warrior who charges through every dungeon, you could easily complete as much as I have in under 100 hours.
But if you're almost living as your character in Skyrim, then it will take a lot more time.

I have a very hard time getting to level 50.
i simply can't find more things to do at level 47, as I ropleplay and limit my questing. But I don't find it to be fun to play a game simply to eat and sleep and such, I do that alongside with other things.
Simply dungeoncrawling gets tedious after a while, especially when I have been to almost all of them already.

My first character clocked 350+ hours. I played as a stealthy ranger Khajiit, and as a previous poster said, I would sneak when "nervous" or when I suspected something was "out there" and I wanted to get a closer look without being noticed. I'm pretty sure my sneaky habits inflated my play time significantly. I almost never left sneak mode when in dungeons; that adds a lot of time to the experience.

I'm also remembering all the times when I'd wait patiently, arrow nocked, for the perfect shot to line up as a bandit patrolled past me (for example). All those minutes add up eventually!

232 hours and I have only done the Companion's quest line and a few of the introductory quests for the other guilds. What's the rush?

Depends on playstyle and how thorough you are in your exploring. Do you find a way to jump up on every ledge or outcropping? Climb every steep icy slope? Do you play a very slow careful sneaky type or just berserk your way through all situations? Do you use a torch and carefully search every crevice for hidden goodies? Do you fast travel everywhere or not? Do you do all side quests you come across? These all multiply your game time.

Easy. Don't rush through game. Explore all there is to explore.

I have over 200 on one character. I have 5. Wanna fight about it?

220 hours in. 30 dungeons cleared. Not joined thief guild, done first quests of mage, companions, bards guilds. Main quest as far as Kynesgrove. Not taken sides in civil war. Not really explored Markarth or Falkreath yet. Quite a few side quests done.

The only issue with playing like this is leveling. I'm level 54, I fear nothing. I'd rather still be level 30. So I only use steel now and 1 enchartment per item.

Perversly playing on master levels you up far to quickly, the more hits/spells you have to strike/cast means more XP. Master should also cut XP awards by 90%. Then playing for 300+ hours can still be rewarding and challenging.

An imagination helps.

Im at 170 hours on my first character. TG and DB quests done, all the daedric quests I wanted to do are done. Its mostly been exploring and chracter building. Lvl 52 n such. Lots of misc quests thrown in there too.

I just love this series a lot so I play the games constantly lol.

I do an awful lot of gathering and literally clear every dungeon of everything that will sell for a gold piece! I have also not been using the map a whole lot which means I get lost and sometimes I forget stuff and have to go back and forth to places. I have a very easy going playing style and I never rush anything I like having little moments when I am in work thinking "Hmmmm what do I have to do later in Skyrim." It's a very pleasurable experience for me also without Fast Travel or Carriages. This is easily my best gaming experience EVER!

Picking flowers takes up lots of time.

I notice the OP talks about his "latest character" having done so much in such a short time. Well, I guess if you have played before then its possible to move much faster if you want to, after all you'll know the locations and the solutions to the problems.

Speaking personally, I am still on my first Character (though he is about to retire) and have logged nearly 500 hours, done 100 quests and found 325 locations. Playing a sneaky type with a personal rule to minmise reloads meant that at lower levels I often spent 4 or 5, real-time, hours to get through one dungeon - the prize was to get through not only without being killed but without needing to drink a healing potion yet still killing everything down there. My next character, who will be kicking in doors and shouting, "Y'all know what this is!"* before laying about him with a great sword, will move through locations a lot quicker.

*Copyright The_Jackal, poster of this parish.

Well, I decided to keep my first charter for awhile. So far it has 800+ hours.

Though if I start another play style, I'll usually put in 100-200 hours into it. Always nice to see the different out comes of all the quest.

No it don`t, I can run and pick without stopping!

I did 1600+ hours on a Fallout 3 character, just to stretch the game system to its ultimate...eventually, nearly every random encounter was multiples of either albino rad scorpions or deathclaws, and some of those enclave or mutant camps were spawning 2 or 3 dozen occupants. The game became impossible to play due to the level-scaling effect, which hopefully won't happen as much in Skyrim.

Explore explore explore, the more you explore the more side-quests you find which creates more to do! (wow that was alot of explores wasn't it?) My first and only charachter, a level 48 Wood-Elf Ranger, so far just clocked up 195 hours, completed the Civil War questline, Mages Guild, and Companions quests and is just sinking his teeth into the Thieves guild quests and MQ now! Soon I will make a female pure mage to have fun with the magic in Skyrim, the most my other chachter did was cast fire spells because he specialized in stealth, one-handed, light-armor and Bows (all at 100).

I can hardly get anything done in 100 hours. 200 is a good start. I have no idea why I'm so slow. I'm having a great time, though.

its called taking your time and enjoying the game...exploring..rp'ing..

I have to agree, I don't mind roleplaying a character but going more hardcoe is mindboggling. That's only my opinion and I'm not condoning anybody who wants to do that.

I noticed that my level 48 Ranger gets hit with more and more nasties now he is higher level, I tried to do a Thieves guild quest today and got hit with no less than 10 Draugh Deathlords at once then a Draugh Overlord , having a stealth charachter I had to do ALOT of backpeddling!