I live pretty much on the equator, I've had an N900 for several months, it has been clocked to 1GHz the entire time. The only time it ever feels hot is if I use mobile hotspot or some errant process starts using 100% CPU. In either case, the correct response is "Meh..." The processor is clocked to 600MHz simply because Nokia is (too) conservative for reasons only they are aware of. In short, the thread starters warning, nice as it is, is simply not required. There is a long discussion here that asks if anyone has killed their N900 from overclocking - result: nobody has.