Reported on pocket-lint by Duncan Geere(link below) is the flood of battery life issues complaints of iPhone users after the 3.0 firmware update.
According to a user, the update seems to use 10% of battery life per hour and if you'll put your iPhone near a speaker, it will register the signals that is being constantly transmitted or received on the GSM radio.
Some users point the problem in the push functionality of the update that causes the rapid drain. Some user believe than turning off all of the connectivity functions of the phone will somehow resolve the problem.
Link: iPhone battery life complaints flood in