As The Hitchhiker's Guide to the Galaxy says on the cover in glowing letters with an unusually friendly font:
There is evidence that some phones are charging at the wrong voltage. A symptom is heat.
Not all heat indicates a problem. High heat while charging means you should monitor charging voltage.
I'm keeping mine. But until Sprint/HTC chime in, it's socially responsible of us to gather community data and awareness. In my opinion.