I always dutifully power down when it is announced to do so although once or twice I have had to be prompted as I tried to get a last minute e mail to send but I always do it if for no other reason that I don't want to be the dummy whose phone goes off just about the time the plane begins its take off roll. That must be embarrasing for those folks-I hear at least one a week.
When I power down I always turn off the radio first so that I can power up and work with it during the flight and I have never seemed to have been noticed by crew.
Now, that said, twice recently after powering off-which usually occurs at the gate when the cabin door is shut, sometime during the take off roll, my BB vibrator bumped me. First time I embarrasedly jerked it out of the holder to turn it off (thinking I must have forgotten, and trying to beat the first ring after the initial vibrator bump) only to find it already off. The same thing happened to me within days on another flight with just about the same timing. This time, with the earlier experience in mind I knew that I had turned it off.
Anybody got any ideas what would make a BB vibrate when it is off?