I joined to mention that I'm also having serious lockup issues with the new Avast 6. It downloaded automatically yesterday, and when I rebooted my computer it froze up at the startup: nothing loaded, no firewall, no AV, no Spybot, my three essential startups. I could open Firefox, or anything; I would get a message after a few seconds that I might not have administrative privileges to do this asction--but I AM THE ADMINISTRATOR! So I uninstalled Avast 6, reinstalled it again, didn't need to reboot apparently--this time, no problems (I guess since I didn't have to reboot, for whatever reason). The day went by just fine. But then this morning, I turned on my computer, and the SAME THING HAPPENED. I've had to uninstall the damn thing AGAIN in order for anything to get working, and I had to do it by going into Safe Mode. Also, the Task Manager wouldn't open for me; apparently I didn't have "Administrative Privileges", again. I really hope this gets taken care of very, very soon, cuz I've been using Avast for years, literally, and I don't want to have to turn elsewhere for my AV needs.
So I've got Windows 7 Ultimate x64 (no SP 1 yet), boot up with Spybot Search & Destroy, Online Armor firewall. Plenty of RAM, plenty of HD space, plenty of everything.