After a number of recent press stories, especially this one, I finally decided to install antivirus software on my MacBook Pro. I went for the Mac version of Sophos, which is free for home use.
My MacBook Pro is a couple of years old, has traveled the world and been on countless networks during that time. With that in mind, a virus scan revealed a grant total of zero viruses. I doubt I would be able to say that for a Windows laptop with no AV used in similar circumstances.
Although Macs are still a small percentage of the total PC market, I guess the rise in iDevices and the lack of people running AV software on Macs makes them an attractive target. Time will tell if they become the attack vectors everyone is predicting.