Depends on the environment mostly I think.

When not being used mine tends to idle at a few degrees above room temperature - 36 degrees C right now. (I live in the tropics)

If I watch movies or listen to music, it gets a little warmer, somewhere in the mid 40's.

There isn't a whole lot of information about the environmental operating range - though the L1 & L2 service manual says you shouldn't allow the battery to get hotter than 60 degrees C so I'd imagine it'd be somewhere around that point.

Mine is clocked to 1GHz - I wouldn't worry about it to be honest.