I discovered 2 teeny tiny dents in the composite back almost right in the centre of the 4 lenses. Brought it up to an online chat advisor as the surface of the charger wasn't perfect and I thought it had done the damage. They booked me in for a genius appointment and I took it in yesterday. I really didn't think it was a big deal but the advisor was saying how Apple are interested in any manufacturing defects etc so I went along anyway.
Got there and the member of staff checked over the watch and charger, on closer inspection he discovered the charger was also dented, meaning something hard had gotten between both the charger and watch, and with the magnetic snap, had dented both sides.
He went off to talk to another member of staff and came back to say I could continue using it as it was unlikely to cause further damage or I could go for an out of warranty replacement. Let's just say I walked away quickly!
I'd just like to say that I didn't go in expecting a new watch, it was due to the insistence of the online staff, and had it actually been a charger defect, to bring it to Apple's attention. I was actually more concerned they would take my watch, I've already grown attached!