Interesting enough, I started an new character, played for perhaps 25 hours and level 25, I did not touch the dawnguard storyline at all. The main quest until killing the dragon at the watchtower. Main focus was the thief guild. Lots of travelig to cities to steal but also long trips through the wilderness. No sign of vampires.
Granted I used an mod who prevent vampire attacks in cities but it was plenty of them in the wilderness during my last game also a lot of wanderers in cities.
This makes me wonder if it's an trigger to start the vampires?

I'm rather whelmed by it all, personally.

Yes no walls and Faendal hunt a bit east of it so he might run into bears or other enemies this might be in your cell but past where you can see.

Well, that character of mine is now level 30, with no intentional grinding, and he's been getting around the place a lot..I've had 2 scripted dragon encounters, 1 random, 1 random Thalmor encounter, absolutely no vampires (apart from one solitary town raid that crashed which I think I mentioned), and seen no legion vs stormcloak fights. I've had plenty of assassin encounters, and random thug encounters, and my roads are littered with dead drug dealers. But as I said, NO vampires and only one random dragon.

I'm seriously beginning to think that the first trip to fort DG is the trigger event, despite what a lot of people are saying.

Can pretty much confirm this.
Took an character to level 27 without running into any vampires. Yes I use the moded amulet but it only stops raids on cities, not wilderness attacks or the hooded strangers in cities. Both are common during Dawnguard play.

Conclusion is that the raiding starts with dawnguard and stops then Dawnguard main quest end unless you block the sun.

I have shown up in a town to find dead NPC's and Ash Piles. Most recently in Dawnstar. So I would say that Vampire attacks DO occur when you're not around as Dawnstar isn't so big that you could not notice there's an attack going on.

They definitely aren't supposed to happen like that, they're not designed to.

It could be right before you left the cell vampires spawned in the cell and so an attack occurred?

1. Vampire attacks do not happen when you aren't in the same cell.
2. Open settlements such as Riverwood, Dawnstar, etc only nead to be nearby for a vampire attack to have a chance at triggering.
3. Some closed settlements share cells with other locations, for instance some houses in Whiterun share the same cell as the Ragged Flagon in Riften.

To get an idea of how close you need to be for a vampire attack in a place like Riverwood or Dawnstar go near to it and use Aura Whisper. If you can see red highlights you're close enough for vampire attacks.

As said above, vampires are not the only thing that attack townfolk. Infact well before dawnguard you could easily find ash piles of NPC's in Winterhold upon entering town. The side path to the town is a spawn point, and enemies and townsfolk often fight right at the edge of the shop, leaving ashpiles around the area. You could be well over the hillside at the town or down at the shorefront under the college and never hear nor see the NPC's fight and lose. Other NPC's die anyway for no discernable reason completely outwith dawnguard. Faendall and the bum in whiterun have died on me several times for no reason, often resulting in me gaining an inheritance before dawnguard was even made.

And my statement earlier is not up for discussion via anecdotal evidence. Its a known fact about the game design and how DG is implemented. Vampires DO NOT attack if you are not in the same cell, they cannot as they dont spawn until you do so in that area to generate an attack.

I can confirm this is not the case as I just recently purchased Dawnguard during the Steam sale. As soon as it was installed I loaded a level 12 character who was met with a vampire attack the instant they stepped off the bridge of the College of Winterhold. It was nothing amazing, merely three vampires attacking from the South. Two rushed toward me as I sprinted through town, but they were all killed by the swarm of townspeople and guards before I even got a shot off. Immediately after an Orc in Dawnguard armor approached me about joining up.

I haven't tried any of my high level saves since installing the DLC, so I can't speak personally to the balance or lack thereof as the game progresses.

I've compared pre-existing games to a couple of 'fresh start' games, and there seems to be a bit of a difference. Pre-existing games, with DG installed into them, have attacks pretty much without any trigger. In each of the four 'new start' games I've cranked up, I've had no attacks until I went to Fort DG.

I'm not being pedantic on this point, but as far as my tests have gone it does seem that there is a difference.

I have taken a new character and run him around doing various things and found that even though I never visited Fort Dawnguard I was still getting vampire attacks. Several in Whiterun. At least one in Riften and one in Windhelm. So you don't need to visit Fort Dawnguard to get vampires attacking on a somewhat regular basis. This is beyond the first attack which seems to be scripted to occur early on to alert you to the problem.

Yup, it occurs without even starting Dawnguard. This pretty much makes the DLC not optional which is really stupid.

Sounds like glitched DLC to me. Try deleting and re-installing it, as I've never had an attack before I hit level 10, or anything like what you describe. Hope that fixes the problem for you, I can appreciate how aggravating turbovamp attacks must be

Shown up or have you visited any houses.
You arrive in the town, vampires spawn, you did not see them but enter an shop. As you are out of the cell the fight is calculated and you see the remains then you exit.

I have decide to just delete DG and play Skyrim. Makes for a much more pleasant experience, not having to constantly look over my shoulder seeing if an attack is occuring somewhere and constantly worrying about the best way and best time to enter a city. Plus, my wolves now howl again!

I will only install DG when I am ready to do the quest line straight through without stopping in any cities/towns.

Don't get me wrong. There is much I like about this DLC and I do not regret having it. But I am officially fed up with these vampire attacks on towns and just won't put up with it any more.

My experience to, after installing it I run into an vampire attack on an town with my level 48 character.
Later started an new game, went to level 25 without any attacks, she became an vampire. I restarted the same character from riverwood and has not had any attacks.
Might be some global flag for runing Dawnguard the first time.

Another thing is that in Dawnstar they can spawn on the far side of town from where you enter so you may not notice them. They can also spawn in two different spots, one by the Apothocary, one by the Tavern. Dawnstar is one of the worst settlements for vampire spawns.

Same here, unless I'm doing Dawnguard or my specific playthorugh doesn't care about Vamps then I'm not using the DLC.

I think DG is suppose to be a mediate threat... So if one dose not want to lose accentual NPCs then get out there and end the vampire treat... lol... Now I understand the other complainants. so don't get me wrong... I'm just saying that BETHSESDA did it intendantally...

how are the attacks relevant to the story?

It shouldn't be an immediate threat. Dawnguard should be optional for everyone but no Beth didn't go down that road and instead has no problems destroying roleplays or killing essential shopkeepers.

Alduin is supposed to be an immediate threat. The situation with the eye of magnus is supposed to be an immediate threat. The game is full of people telling you to go there and do this and once. But the game does not force you to react immediately. Because people like to do quests in the order and at the pace they choose. That is one of the big attractions of Bethesda games. So Bethesda thought it was a good idea to release a DLC that forces itself on the player and actively harasses them to complete it at once. With the possibility it will be bugged and they'll still get attacks anyway.

If Bethesda did this intentionally, they have deliberately gone against a feature of their games that's one of the reasons people like them in the first place. That is spectacularly poor game design.

I was relatively quiet on this issue, despite all the complaints on this board, because I didn't own Dawnguard. Having purchased it recently, I held off on downloading mod "fixes" for vampire raids until I had experienced some of them first hand. As I said in an earlier post my first such encounter was stepping out of the college in Winterhold and hardly seemed a threat to my level 12 character. That said, I just loaded up a save of my level 9 mage in Whiterun. Let me make this quite clear, this save is one that was made with Dawnguard installed and with no vampire attacks taking place. I had been outside for some time, and had done nothing to supposedly "trigger" said attacks (ie. no cell transitions, leveling up, etc.). It seems rather strange then that after reloading my save game from last night within two minutes I get a message informing me I've failed the Amren's sword quest. How? I'm just standing here in the middle of a sleepy Whiterun, just as I had left it when I made this save. To top it off, I've actually got Amren's sword in my inventory already; I just hadn't seen him since returning.

Anyhow, my suspicions were aroused given the complaints here, and so I took a gander about the city. A short run revealed some guards in long range combat with vampires near the main gate. I quickly rushed in to help out, but even my quick work couldn't prevent the deaths of Amren, Adrianne Avenicci (who was eventually reduced to an ash pile), and three guards. Conclusion: I'll be installing a mod to prevent these attacks immediately.

Fix'd that for ya.

Personally, I have no trouble handling the attacks with my Dunmer Vampire Lord Assassin, and I get very frequent attacks as well. I like the attacks, and think it lends an air of impending doom over the DLC until you solve either side of the Quest line.

I just find it silly for people to assume that they speak for the whole community, when there is enough dissenting opinion to prove otherwise. And beofre anyone mentions about the number of threads/complaints, that's a paltry .02% of the total number of downloads that Dawnguard has had, so it's not "most people" who dislike it.