I'd like to know more details about this incident. I'm really curious if sweat had something to do with it. Sweat seems to be a problem for many smartphones, and seeing the burn at the battery connection, it could easily be a short circuit due to that.
A friends iPhone3G stopped functioning because of sweat. After drying it up, he had to take it at a repair shop for a thorough clean-up, and they had to replace something. But no burning or anything serious in this case.
BTW, these incidents should be reported, so people can take measures and protect themselves, and companies test their products more. This is not bashing, and the Apple reference is for an incident already reported days ago on Tom's. Good job Marcus for linking it to this article also, so anyone who missed it can get informed.
At least, chargers seem to have stabilised, they used to blow-up while charging idling phones. Batteries need more attention, though.