After years, I've decided that I have found no use in anti-virus software. They are bloated and inefficient software that often causes more performance problems than anything else. A good browser (Firefox is my preference) and perhaps spybot search and destroy are the only two things you should ever need (I don't even have spybot installed anymore).
Surf smart, don't download CRAP (toolbars, etc.), pay attention to what program installers are doing (if there is a checkbox, read what it's doing, more often than not it's trying to install something else), and most importantly, don't install something unless it's from a credible source (opening .exe's from co-worker and/or family e-mails are not considered a credible source). Actually good rule of thumb: don't open executable that come in e-mails.
A company came to me that was having tons of computer issues. After reformatting the computers, installing firefox, and not allowing the standard user the ability to install anything, problems went to zero. You should see some of the stuff I find in the "downloads" folder of the computers. Apparently they are still trying to install stuff... Thank god they can't.
