If you are like me and run the screen at 100% brightness full time, it gets RED HOT in the middle/lower left area within about an hour of continuous use.
Lowering the brightness would likely reduce the temperature..
I have noticed it getting warm from time to time. It's obviously not blazing hot like a MBP and it's not uncomfortable. However, if you use a case you won't even notice. I use a smart cover and when I'm holding the iPad I just flip the cover to the back. No more heat.