I stumbled upon this article today, I think it rather neatly explains why Mac users are so standoffish when it comes to discussing security. The argument that Macs are less vulnerable to attack because they are fewer in number and therefore, less appealing a target, is tired and short sighted. OS X is inherently more secure than Windows, full stop. No operating system is un-hackable, but comparing OS X and Windows (pick XP or Vista, whichever you prefer) is like comparing Fort Knox to my garden shed.
Update: What do you think of this!
Further update: Set your phasers to smug!