Both the 2 iPad 3's I've had, run cool, with no noticable warm spots on rear of case at all, even after being on 3 or 4hrs watching films, same with browsing etc. so very strange.. TBH I assumed and expected it to get a little warmer due to the larger battery and faster gpu etc. but it feels no different to my iPad 1, wife also say she cannot feel any warm spots on the rear case either.. room temp here is currently about 22/23c and the iPad is in a folio case too, but AIS after a heavy session, I've removed it just to check if it was getting warm.. and no.. it's fine.
Reason I'm on 2nd iPad is because I returned first one due to a tiny dust partical on the screen under the glass which was visible, and TBH It was not immediately obvious until you kew where to look, I only noticed it on the 2nd day.
On the subject of weight, thats a none issue for me, at least iPads have a metal case (I think it's metal anyway), the iphones like many other gadgets today definately have a plastic case. I can't really tell that much difference weight wise between any of them..lol tho it does feel a touch lighter than my iPad1 64/3g.