DIVID Technology Riffraff & Whatnot

Macbook Pros now have two graphics chips. One is used to conserve battery life, while the other is used automatically on demand. OS X detects this need per application, and monitoring if an app has triggered GPU access can be found in System Profiler, but there’s another way. Bjango’s iStat menus can monitor power on each GPU so you can tell when the discreet graphics are active at all times, Allowing you to quit whatever app (looking at you Tweetie) is keeping it active while you’re out and about.

http://bjango.com/apps/istatmenus/

Update: This is even better => gfxcardstatus menubar