You can turn it off now, no you couldn't before
If you are rocking a 6G iPod nano a new software update is offered for the device that adds some new features and fixes some issues. The new software version is 1.1 and it allows the user to turn the nano off completely rather than just putting it to sleep.
The user can control the music or radio functions using the sleep/wake button without having to look at the player as well. Turning the nano off will stop music from playing, clear paused radio, and stops slideshows playing on the device. Obviously, nothing continues since the nano is off.
However, if you were using the Nike + setup the data will stop and save before turning off rather than losing your workout. No earth shattering new features, but these are things that I bet lots of users have wanted.