For what it's worth:
My iPod Photo (60G, purchased June 2005) wouldn't turn off either. I nearly always play the iPod docked to a Bose SoundDock external speaker. Yesterday, I lifted it off the speaker dock without turning it off first to take it on a trip. Discovered it wouldn't turn off by holding down pause/play, even for a full minute. No choice but to let it drain until the next day. Back home, I placed it in the dock, let it charge for about 15 minutes, turned it on (it turned on OK), turned it off *while still docked* (it turned off OK), took it out of the dock, turned it on out of the dock (OK), turned it off out of the dock (OK).
Not sure what, if anything, this means.