My One gets warm/hot when I use it for long VOIP calls. It also did get really warm once when I accidentally pressed the 'Record video' button in the camera app and slid it into my pocket. I only realized that the camera was running by how hot the phone was in a little while.
Were you doing anything besides web browsing? What were your ambient temps? I've seen temps as high as that while using navigation in my car, with it charging and with the sun beating down on it. I use a vent mount now and with the AC blasting temps are low.
It's the nature of the device. A solid block of aluminum is basically one giant heat sink. You would be surprised at how much energy is expended (and, consequently, heat generated) changing all those 0s to 1s and back again. Mine has gotten ridiculously hot before, though a straight hour of Beach Buggy Blitz will do that. Look at it this way: better the heat is moved out and dissipated through the chassis than sit around and cook the components constantly.
Yes, it usually overheats when I'm running Google Maps. I've actually had mine tell me that it couldn't charge in the car because the power being consumed was greater than the charge going into the phone. WTF?!?!