we have over 30 9800s here and never saw this on them or the 100s of other BlackBerry devices I have seen at the office.

Lithium batteries have protection in them, maybe it got hot from being in an area with weak signal, mine will do it at a few friends houses as it searches for a signal.

once a OS 5 app was installed on an OS6 devie and CPU spiked to 99% causing it to heat up a bit but not enough to burn me.