I attempted to replace my Edge 500 on my bike mount this morning as I've done hundreds of times since getting it in April of 2010. To my dismay, it fell off and when I checked the mount the two little mounting tabs (ears) on the back of the case were inside the bike mount. My heart sank thinking about having to trash a perfectly good unit.
A brief internet search reveals that more than a few other folks have had the same issue.
I just emailed Garmin product support in the hopes they'll replace it for free. I'll post their response later. Fingers crossed!