I'm still using Virex version 7.2. This was offered when I got my dotmac account some years ago. I've never upgraded to a higher version, although I do update the definitions once per month. I do this as a courtesy / precaution for my windows-using brothers and sisters. On occasion, I'll scan my system with it, but nothing has ever been turned up. Apple stopped their support for MacAfee Virex (and its inclusion in dotmac membership) some time ago. Just as well, as the latest versions of Virex have been known to slow down systems and wreak other havoc. They keep adding stuff that no one wants or asked for.
Many Mac users swear by the free BSD package, ClamXav. Most people say the price is right, and it simply works the way it should, without a lot of extra nonsense. I'll probably go with that on my next Mac.
As noted, most companies, the government, and college / university IT departments mandate that each and every computer on the network must have anti-virus protection, regardless of what operating system it's running.