This may or may not have something to do with the problem. I was having trouble with my restore points getting corrupted and not able to be defragmented nor removed. I found that the problem was not being caused by Avast but by, get this, Office 2010, in particular the starter edition that came preinstalled and that I had activated. Searching around, I found that the problem can also exist in the full versions of Office 2010. It has to do with that mysterious Q drive that Office creates to enable the new virtualization features of Office 2010. It conflicts with the Volume Copy Shadow Service in Windows 7 and causes restore point corruption. I removed all traces of Office 2010 and installed my old developers edition of Office 2007. It installed, fully updated, and causes no problems with System Restore at all.
I don't know how many of you use Office 2010 but if you do, it may be causing problems.