A little bit of buzz has arisen after Apple has quietly suggested and recommended to Mac users that they should consider installing anti-virus software on their Macs. This has created somewhat of a stir since Apple has said several times that Macs are far less susceptible to viruses if they even get them at all. Personally I know that viruses can be written for any platform, Windows, Mac, and Linux alike. Windows just is the primary target since Windows holds the greatest market share...by a lot. Now imagine if the tables were turned and OS X held 90+% of the OS market, I'd bet that instead of Windows getting the majority of the threats, OS X would likely take the brunt of the attacks. Simply put, the evil-doers will go after whatever they can get the most out of.
I'm one of the people who has a Mac but doesn't have anti-virus software for it, which is probably not exactly the smartest move, but for the moment, I haven't needed it (or I've just gotten lucky). OS X doesn't have a lot of viruses in the wild that can affect the OS, but this however may very well come to an end soon enough with how popular the Mac line has gotten, and how OS X is rising which might make it a much more appealing target for virus writers. It might also be worth noting that Apple's switch to Intel CPUs a little while back probably makes it a little bit easier for the writers as well since they're so used to that for Windows machines.
In the end, I do understand where Apple is coming from, despite what they want to say, they have to acknowledge that OS X is not immune to viruses, no OS is (not even Linux). So putting anti-virus software on a Mac is by no means a bad idea, we'll just have to see how Mac users react. Will they snub their noses to the thought or will they think about it and agree that its probably a better idea to be safe, rather than sorry later should their Mac get infected.
One last thing for everyone to consider: Apple has been consistently growing, sales are up and more and more people are bringing Macs into their homes. With this growing popularity, comes a greater target. The number of threats are only going to go up, stay vigilant and be careful what you download, what you install, and what sites you visit. OS X may be a "small" target today, but given the growth, I don't know how long it will stay out of the virus spotlight.