dvandom

While it's starting to get annoyingly slow, I've never had to do a full re-install on my 6 year old iMac. And Macs aren't so much immune to viruses et al as protected by species barriers. A Mac is no safer against a Mac virus than a PC is versus PC viruses, but there just aren't enough Mac viruses to cause concern, and they can't catch each other's stuff (leaving aside things like macro viruses).