I hope I mean no battery drain. I just made that change today so I haven't had time to test it, but I'm fairly sure it really is going off... it might still be trickling current for the clock, but it shouldn't be running the OS. I'm going to try to use it for a while like that to see if it prolongs the battery life in any significant manner.
I tested it with my current book and it remembered the current location as well as a test bookmark. I don't use bookmarks much so if you're concerned, I'd connect to Connect (heh) before you start playing with it just to be sure.