I just had this happen to me yesterday.
I always keep GPS off, but turned it on yesterday when I was looking up some things. I did some web browsing, and noticed when I was done my Razr Maxx was very warm. I started freaking out!
I turned the phone off for aboput 30 minutes, it cooled it down a bit then after turning it back on it started to heat up a bit.
I tried to figure out what I did to cause it, and the only thing I can remember was turning on the GPS. So I turned OFF GPS and the phone cooled back down to it's normal level.
So for some reason, having GPS on, even though I wasn't using the GPS anymore was heating the phone up for some reason. I dunno why that happened, but problem solved...atleast for me.
Thankfully I hardly ever use the GPS in the phone. But now I am wondering if I want to use it if the phone will always heat up like that.
Strange.