Man... remember when people use to pay for antivirus? Last I checked you really don't need antivirus if you have a decent firewall, keep your OS up to date, and don't click on things you ought not to. And now there is Microsoft Security Essentials, which while not perfect, doesn't have much of any performance impact, catches almost anything that for-pay AV will catch, and is FREE!
I do understand the need for added security on servers, and things which attract more attention from thieves, but for the average home user I find that if they are determined to catch a virus through some smutty site, not amount of AV will save them.