I had this happen to me as well, Monday, at the gym. It was bouncing around in my pocket as I was doing cardio on an elliptical trainer. At some point, I fat fingered the karma to skip to next track and it just locked. Spent 13 minutes w/ no music.

Paperclip from front desk fixed it, but battery had run down to 3/4: I suppose the drive was left on during the lock.

I'd really like to get an armband as I think there's less jarring near my shoulder joint vs. my pocket for what I do.

Edit: don't think mine did a DB rebuilt though: it booted up pretty quickly

-brendan