I've got nothing to productive to contribute to this conversation other than I've noticed this too.
The phone will be unbearably hot to hold. I've tried to see if any application were running in the background, eating up resources, but there's nothing consistent that I can report. Some days my phone will go all day long without any problems. Other days, the phone just drains the battery really fast, gets really hot, and displays an over-heating message. The only thing I've been able to do is shut the phone down and remove the battery and wait a few minutes until it's cool to the touch, then put it back in.