my two personal experience with Avast.
1st-
i had installed it on my Cousin's laptop (1.5 yrs ago), initially it worked well, but after sometime (15hrs), it completely SLOWED down the lappy

.
the lappy b'came so slow that, boot-up time was near 15mins, when i click on "Start" menu it took 2-5 mins to show up
i thought some virus is causing this, so tried to scan it, but Avast took 10mins to open

, so i just dropped the plan & also dropped the Avast.
First i removed its start-up entry frm
msconfig, at the next re-boot the system came back to its normal Speed.
there after i installed AVG Free on his lappy, & he's usin it even today
2nd XPerience
just few week ago i had a p-rated XP Pro on my system (non SP2). so to install SP2, i had to visit some "You Know What" (YKW) sites

for "You Know What" things

, i d/led a YKW thing & scanned it with Avast, then Avast said its
"All Cool Bro" go ahead & do what you want.
so i opened the zip file & opened that app., that app. dissappeared when i double clicked it loool

.
now i think you know what that YKW app was, - a trojan
now i cursed & cursed & cursed that cr@p Avast sooooo much.
then somehow i installed Kaspersky Internet Security 6 (frm Chip DVD), coz internet got screwed, Internet Explorer got raped

.......the screwed list goes on

.
after KIS scanned the whole system it found
11 "High warning" virus & 7 Trojans. ( i remember installing
ONLY ONE trojan

)
So Avast is a BIG No-No for me.
on the other hand, i used to have AVG Free before KIS, at that time also i used to search for "YKW" for games

, but AVG stopped all of bad YKW, & when i installed KIS (very first time, after AVG), it found only 2 Virus/trojan.
IMO even the old AVG is far more superior than that Avast.