I usually don't turn my camera off when I'm done shooting... just in case something would happen in front of me I like being able to just start working and not fumble with the power switch. The startup time, which is admittedly still pretty fast, takes longer than coming back from standby.

The other night I was driving back from a basketball game and went over a couple sets of tracks at a railroad crossing. I must have gone over a little harder or faster than normal, because it bumped my camera just enough to reposition itself and sit right on the shutter button. I now have 154 photos of the side of my camera bag... thought it was kind of funny.