I tried avast when my nod32 license ran out which I think was 6 or so months back it was still v6.x.
Whilst I didnt find it perfect (what av is?) it generally worked ok.
But then v7 came, it wreacked havoc on outlook (other users confirmed bugs I found) and then when I did a upgrade on the avast on my laptop from an older v7 to newer v7 the av on it completely broke, hanging boot etc. with the avast service stuck, so I eventually gave up on it and now my laptop has mse and my main rig is back to nod32. I do still wonder why I use a/v's tho as they are buggy and slow things down, and once in a blue moon it may find something thats not a false positive or not something I already know about.