We don't use Anti Virus on our company workstations - we all run Macs, and we're all pretty sophisticated power users with various high levels of security know-how.
I don't use Anti Virus on my home systems either. I use NoScript on Firefox which prevents drive-by downloads, and I always check MD5sums of downloads, or only download from sources I trust. That said, I don't download a lot of software anyway.
I have my wife trained to use NoScript with Firefox, and she doesn't download anything without asking me first.
I haven't had a virus infection on any computer I've used in over 12 years - when I got an infected floppy disk from a classmate in a college project.
User training is the best Anti Virus you can implement in your company, and your family household. It is well worth the time-cost, and will save you money since you don't have to buy AV products.