Pretty neat concept. Certainly better than the wristwatch equivalents.
From a QS perspective, I'd like to easily visualize how much I've moved during sleep. Some nights I wake up in the same position I went to sleep in (hence the expression "sleeping like a log"?), with the comforter in almost the same place and orientation. Other nights I move. I wonder if in the first case I don't move at all, or I do move but return to the initial position.
On a final note, I know of two other solutions that work without touching the user:
1. Apps that sense your motion via the mattress if you leave the phone on the bed
2. GentleAlarm for Android, which I find quite brilliant, and which works like this: