There are no unalloyed joys.
You have to have a .Mac account to get Virex as a "civilian." Unless
you buy a 5-pack. But I never had problems with updating Virex
defs. Don't use the built-in auto-updater. Just go to versiontracker
and download the defs file each month.
Norton's auto-scan has an interesting effect on PowerPoint 2004. You
can't save a presentation (with the same name) if autoscan is on.
ClamAV is free, and (my opinion) worth every penny. It is beastly slow
on my G4 867DP, it won't scan more than one volume or more than
one folder automatically, it doesn't scan downloads on the fly, and
there is no way I could find to see what exactly it protects against.
Other than that, I guess it's OK.