I traded in my first gen iPad for store credit @ BestBuy yesterday morning and bought the new iPad: in white, 16gb, wi-fi model. I turned it on w/o charging and noticed the battery was charged pretty well, so I did decided to set it up as a brand new ipad, no loading of any back-up. After set-up, I used it and allow it to drain to 0%. During that time, I downloaded some apps, browsed the web and used some reading apps like Flipboard. I noticed the back of the iPad felt a bit warm, but I didn't think much of it. Later that evening, I cranked up the brightness like I used to on my old first gen iPad. The device got uncomfortably hot while I held it in landscape mode. I tried using it with the smart cover flipped back so that I wouldn't be touching the iPad's back directly. It's not an comfortable and I haven't tried it out again because I have been charging the ipad afternoon and evening.
That's another thing i'm not wild about with this new iPad. I have to turn the unit off for it to get a steady charge with the battery adapter that came packaged in the box. If I leave it on while charging from a wall outlet, it's incredibly slow to charge. I didn't realize that until hours after I started charging.
Once it's fully charged, i'll test out the heat issue with the brightness turned down halfway, auto adjust brightness set to off, and with bluetooth disabled.
I'm seriously considering returning to BestBuy in a week to exchanging the new iPad for an iPad 2 if these issues continue. It's a shame, because i really like the retina display, but I don't like the heat it gives off or the fact that it charges so poorly when the device is on. That wasn't the case with the old ipad, my old iPhones or the most recent gen iPod Touch (the ipod touch does get pretty hot when running games like Scribblenauts, though).