The big one I'm worried about is the random vampire attacks that can depopulate entire cities.Has anyone seen this starting to happen on the PC version?

Probably needs to be posted here:http://www.gamesas.com/forum/199-pc-hardware-and-software-support/

Yes, I find this disturbing as well. I feel alone enough in Skyrim. I think I'll try adding my SIMM or SIM.. whatever, the travelers mod. It adds a lot of tough people to everywhere. Maybe they'll protect the cities.

When I went to Dragonsreach/Jorrvaskr, I saw a riot going on. Running to it there was Master Vampire and their Vampire Thrall, they had already killed several civilians before the guards could occupy them. I'm going to setessential 1 the town NPC's.

The attacks are supposed to happen, just not frequently.

Yep. I went to Riften and as soon as I made it to the central market some Vampires had killed 3-4 people.

I'm aiming to just get through the main quest line without entering a major city during it. Gstaff claimed the stop after the main quest line is complete but we'll know soon enough.

they die anyway if you enter or no, and that is a problem

You will first see an unofficial fix for the bugs by the community and later Bethesda will copy this fix and make it their own and release it as official.

The Vampires are only triggered if you enter the same cell. A problem with this however is that some areas share the same cell.

yeah i been losing ppl in place i havent visited and isnt a problem when they are guards or other NPC no important but this attack are breaking NPC i need for my quest in vanilla Skyrim and is pissing me off

Dawnguard will not be patched. Not by Bethesda. But the community will pick up the slack, eventually (on PC)...
In the previous game, Oblivion, none of the DLC content was patched by Bethesda.
Eventually, the " Unofficial Official Mods Patch" project corrected a huge number of bugs, in Bethesda's additional content for Oblivion:
The Unofficial Oblivion Patch, Unofficial Shivering Isles Patch and Unofficial Official Mods Patch are major mods by Quarn and Kivan that fix over 1,800 bugs (and 70,000 object placement errors) left over By Bethesda!
These fixes range in importance from trees that seem to float in the air up to conflicts that could cause the game to crash....