There is much to be said for your experience, 'V' (I like that show.)
I had Zone Alarm Extreme Security on my Windows 7 64 bit and it 'borked' IE8 with lockups, Opera 10.5 with system hard locks and Firefox 3.6 with various maladies. I ended up re-loading the OS and keeping all the apps I use as Microsoft only, with the exception of 7Zip. I have been rewarded with a stable and fast OS, with a stable and responsive IE8. AV is handled with MSE and my disk maintenance and backups are handled with the on-board tools.
My lesson re-learned, is that no one knows an MS operating system better than Microsoft. This time, the lesson only cost $50 and a bit of time.