For some reason my Nano doesn't want to turn off anymore. I dutifully held the play button like I used to, but alas, no love. I did a reset and nothing changed. I had taken to just leaving it plugged in except for my runs and commute. This morning, I finally did what I should have at the beginning.
Gooooooogle to the rescue!
A quick check of google led me to a Cnet forum where some other folks had the same trouble. The workaround is to pres the menu button to the top of the menu tree and then (and only then) will you be able to turn the Nano off like normal.
I tried it and it worked like a charm. Very strange that I can't turn the thing off normally like I used to, but I'm happy that I can actually turn it off at all.