I used to be in the camp of "don't bother." I had no problems at all without it. However, while I was in charge of an all Mac network a few years back, a bunch of our customers were getting hit with virus laden emails from our Customer Service Team. It appears one of our vendors sent us an infected Word document that we in turn passed on to customers. It never gave us any fits but sure ticked off a bunch of customers. We started running AV software right away to protect our customers and therefore ourselves.

There are fewer than 50, last I heard, viruses in the wild for Macs at this time. The chances of you having problems are quite low. If you have AV software available to you use it to protect your friends and contacts from viruses that you may pass on if nothing else.