From what I gathered from the past 6 months, if you don't use a brand new Win 7 (or else) installation, or if you previously installed then uninstalled other well known security anti-malware softwares, you will 98% certainly have great problems with AVAST 7, even 6! I mean, I don't have these problems with AVIRA and it runs smoothly, fine and well and I tested on my pc without formatting 4-5 AVs... Come on, stop being blind and do something...!!!
What total rubbish.
I have participated on every avast beta (bar one), pre-release trial and regular program update of avast since I have had the XP Pro system almost 4 years and never once have I had to format my system.
On a very rare occasion have I had to do a clean install as opposed to an in place update (one of the pre-release betas). I have never had a major issue in all of that time, I have some minor issues, but they too have been resolved.
As I have said before "Don't lose sight of the fact that this is a support site." with over 150million active users with multiple system permutations, you are likely to get some who will experience problems. The point is that for those who want help and are seeking it (not just venting), there are people prepared to help.
In almost 8 years participating in the forums I have never seen or found it necessary to recommend that someone format their system just to install an update. So I have absolutely no idea what is going on with your system or why you just felt a format was your only option.