I have used Avast on this machine for as long as I've had it -- over 2 years. It has been the only one I've ever run.
I also run SpyBot and have for years.
One thing I noticed last night and fixed this morning -- the windows icon cache was corrupted, and after following the directions on Microsoft to delete it and reboot, Avast seems to be behaving itself again. So that may have been the root of my problem all along, not Avast.
Re: captcha -- even though it's only displayed for the first 3 posts, you really should try to replace it with re-captcha. The style you use is extremely hard to use -- the first time I saw it, I got it wrong multiple times.