I have AVG version 8.0.101, the freebie one.
Some people have had probs. with this, but if you read the installation/users guide and work it properly there are bo problems to be had in it's operation.
There is an issue at the moment in that AVG is conflicting with spywareblaster and the immunisation feature of spybot search and destroy in that AVG is reporting as "warnings" the defences that these progs have put in the registry.
AVG appear unwilling to change their prog to accomodate this issue, but the conflict is easily avoided (if you have either or both of the progs installed) by disabling the spywareblaster protection and the spybot immunisation for the duration of the AVG scan, then switch them back on.
AVG version 8 now includes anti-spyware as well as anti-virus resident protection, as well as mail scanning, link scanners etc.
It does use a bit of resource, about 40mgbs of ram whilst working in the background and about 26mgbs of HDD space.
If you go to
http://freeforum.avg.com/read.php?13,122766,backpage=,sv= and follow the link therein, you can download an AVG user manual as a pdf of about 3mgbs.
I like AVG and have had no problems with it, and reckon it is as good as any other freebie, better than some and better than some of the paid for jobs.
Others detest it and would recommend Avast.........which I think is every bit as good as AVG in detection rates and is currently without the spyware conflicts mentioned above.
I think it is a case of trying and seeing which you get along with.