I have a 2008 MacBook Pro (last one before the unibody ones) and have been monitoring a the laptop temperatures for almost a day. I used Temperature Monitor to graph the changes in temp and correlate them to my typical usage.
Aside from obvious considerations (GPU getting HOT while playing 3D stuff), I noticed that when I unplugged the laptop from the AC adapter the temp dropped down by 15-30 °C.
I think this may be related to some energy-saving mode of the CPU/GPU but I didn't find any setting or hack that allow me to turn it on on purpose. Is there a way to do so?
PS: One may ask, why do you care about temperatures: well, first of all it's summer and this laptop is damn hot. On the other hand, I'd much prefer my laptop to use only as much resources it needs for common tasks and then turning it on when I need more computing power.