It happens around this time every year -- some company that makes its money from security computers claims that next year will finally be the year the Mac goes under attack from virus programmers. This year it's McAfee, who are claiming in a report that due to the popularity of iOS devices, Apple will become a "prime target" for hackers and virii in 2011. As you might expect from a company that sells anti-virus software, McAfee claims that its research shows "threats of data and identity exposure will become more pronounced," especially on the Mac. Go figure.
That's not to say that you shouldn't be careful about your computer -- always stay away from sketchy websites and browse as securely as you can, always use secure passwords, and always keep your Mac up to date with the latest patches and fixes, just in case. I'm not even saying that all anti-virus software is a waste of money -- there are some good worthwhile solutions out there if you feel they're necessary. But the anti-virus folks have been predicting Macs will finally get threatened for years now, and Apple's platform is still much more secure than most others.