If you have the developer tools installed, in /Developer/Applications/Perfomance Tools there's an app called Spin Control that helps diagnose why apps are spinn

If you have the developer tools installed, in /Developer/Applications/Perfomance Tools there's an app called Spin Control that helps diagnose why apps are spinning. By default it just sits there waiting for an app to spin for 5 seconds, at which point it starts sampling the app's activity (as in sample(1)). You can set preferences to make it watch a particular named app, and can set the minimum spin time required for it to notice and start sampling the spinning app. The app produces a text report of the output so you can see what functions it's spending its time in. Might be useful. It seems like you shouldn't be spinning that much, even if you're multitasking.