Currently, my 15" 1.5GHz PB is running at 56C (processor bottomside), and I've only got Safari and Mail open... I had X-Plane on earlier, and it peaked at around 62C. The Processor/Controller Bottomside is one degree more at both times.
According to Temperature Monitor, the maximum limit of the processor bottomside and processor/controller bottomside is 75C and 76C respectively.
Also, I don't get any instabilities running at over 60C - I just get a very, very warm desk! The desk feels warm if I put my hand on the underneath!! 😱