As a Mac user, heat is nothing new to me. My iMac will easily get up to 70 when rendering before the fans kick in, but that's normal. I usually keep my fans going a little faster than normal, especially my HDD fan (for some reason, HDD's run very hot on these computers, and hot HDD's are not happy). When rendering on Mac Pro's, I find the temp usually doesn't go above 45, but that's because the Mac Pro I've used is liquid cooled (which is awesome).
Honestly though, I've never had any trouble with CPU heat, even back in my PC days. It's the HDD enclosure that's always made me nervous.. I've blown at least 4 HDD's, all from heat-death
As others have mentioned, getting dust out of there can help tremendously. If you're in a hot climate, that can always cause increases in heat too. Here in the Canadian climate, my computer tends to run a good 5 degrees warmer in the summer months than it does in the winter (when doing nothing intensive).
