I've come across postings elsewhere that seem to say that AVG 8 can cause serious damage to your PC. If I understand it correctly:
1) If AVG 8 finds a virus it tries to put it into the vault (OK so far)
BUT
2) if the infected file is part of a larger 'archive', e.g. your Inbox with loads of other messages, then AVG 8 moves the whole 'archive' to it's vault (not fatal but getting awkward, to find all you mail has disappeared when only one mesage is at fault)
BUT (the real killer)
3) If the 'archive' AVG is trying to move is over 5Mb then instead of putting it in the vault it deletes it (oops, there goes your Inbox <img src=/S/toilet.gif border=0 alt=toilet width=24 height=26> )

There's a relevant thread here:
http://freeforum.avg.com/read.php?12,132268,132279

Ken