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.
Since I got such a big productivity gain from this change, I'm looking for other things I can do. I'll be due for an upgrade in another 4-6 months and I think I'll get an SSD.
I almost have to admit that the 9 window limit on the iPad's Safari isn't a bad thing. Forces me to instapaper stuff right away and close the window.
Friends and family literally have literally made a novelty of exposing safari when they come by to wonder at how many multi-tabbed windows I have open at once. :)