After doing a clean install of avast! Free Antivirus v7.0.1407 yesterday, I got a couple of crash errors after the first reboot.
One of them was xboxstat.exe (I've got two Xbox 360 wired controllers for Windows connected)..
..and I think the other one was a Visual C++ error of some kind.
I did another reboot, without any errors, so I thought nothing more of it..
..until today, when everything just seemed to behave slower and slower.
I got not-responding-errors for just about every program I was running (first for explorer.exe, then for opera.exe and so on..)
I tried a reboot, which almost brought my system to its knees waiting for avast! to start up.
After this, I uninstalled v7.0.1407, and did a clean install of v6.0.1367..
Now everything runs fast and smooth again!
I've been using avast! for many years, so I'm familiar with decreased system performance when all the "unnecessary" real-time shields are enabled, but that kind of bloat can't be compared with the near total system failiure that v7.0.1407 caused..
To preserve system performance, I've always had all shields disabled, except for the File System Shield itself.
I've never used any of the additional protections either, so this should rule out quite a lot of possibilities when it comes to tracking this problem down.
(Running WinXP32/SP3)