I sometimes use my iPod video’s Sleep Timer. One nice side effect I found is that the Logitech speakers I use also turn off it is on battery power (vs. plugged into a wall socket) after the iPod shuts down. One oddity, though, is what happens the next time I turn the iPod on, it immediately turns off again. This only happens once though. However, I remember being surprised the first time I noticed this.
I’m not quite sure what the cause of the other iPod sleep problem I’ve noticed. That is, every once in a while (perhaps a couple times per week), the iPod won’t turn off the usual way. I found that locking and then unlocking the iPod (it starts out unlocked) restores the ability to turn off the iPod.
I’ve never used the iPod touch’s sleep feature since doesn’t work with the dock on the Logitech speakers I have.