I just found a really great app called gfxCardStatus that works with any 2008 or later MacBook Pro. It is a menu-bar app that shows you which GPU is currently being used. Keeping it down to the Intel GPU decreases the heat generated and increases battery life.
I was amazed to find that one of the apps I always have running, NetNewsWire, switches to the Nvidia GPU when running. Which means my usage pattern was causing a lot of heat and reducing my battery life.
Another great feature of gfxCardStatus is that you can turn off dynamic GPU switching and force a particular one to be used. I’m leaving mine on dynamic for a while, just to see which apps cause a switch. But I imagine that soon my normal procedure will be to disable dynamic switching.