I have two Apple laptops, one running Snow Leopard and one running Lion. I love them to bits and no, I don't have antivirus running on them, that's not to say that it isn't possible to get a virus (and to be honest, I need to update myself as to where OSX and virus's sit these days) as just about everything is possible, I just evaluate the risk/reward with everything I do and for now I just use the firewall, run in stealth mode and no antivirus.
The Archangel