Leave em all on. I think anyone who tries to micro manage these settings is wasting time....
The GPS only gets used when an app needs it.
Wi-Fi takes WAY less energy than your phone attempting a constant connection to a far tower.
Bluetooth only activates when you are near your car.
Etc...
I leave them all on.
Great Topic buddy, also to add to that WIFI is a major killer as well. I notice when I shut off my wifi and GPS location my phone is a complete power house and it lasts all day. Wifi is a major battery killer no need to have it on if your just chilling with the family or running errands. But great suggestions. ALSO DROID IS THE BEST PHONE IN THE WHOLE WORLD.............UNTIL DROID 2 COMES OUT LOL
I believe using WIFI will actually conserve more energy as opposed to just running it off 3G.
EDIT: Maybe this is just when browsing, and keeping it off otherwise?