As shown in these two pictures, the temperature went up about 10C after I turned on iTunes visualizer (Jelly) for 11 minutes. Anyone noticed this?
I am afraid that I will never turn it on again.
Check out your CPU usage in the activity monitor and you will find your answer. 'Little' graphical programs like this tend to put an extra burden on your system resources.
Visualizations put huge strain on the GPU - the amount of processing power required is pretty amazing.
My MacBook Pro (when running under Windows XP in BC) will be going full blast when I use the Winamp Milkdrop visualizer (which is far the best one out there).