I have the iPad3 64gb/4g model, and no issues with over heating either, this story appears to have been leaked or picked up by a couple of newspapers today in the UK including the Daily Mail, with the headline 'Burning Apples' which is typical over dramatising and stupid reporting by this paper. However, it did prompt me to slide mine out of it's folio case, just for peace of mind, and feel the rear of the case, I'm pleased to say, mine feels totally cold to the touch all over the back case, it doesn't even feel warm.
Temperature in my room is 23c and the iPad has been on for over 3 hours now, mainly streaming live TV, while I'm at my PC, and it's also in a full folio case. Maybe some users are in quite warm rooms or where ambient temperature is fairly high and likely have the brightness up quite high, or simply just have faulty units, though TBH I suppose it would be reasonable to expect the iPad 3 to be a touch warmer than the prevous iPads..but I'm not seeing it here, mine's not even getting warm.
Brightness setting is just under 50% with auto brightness enabled, it looks just right 'brightness wise', and AIS it's actually running quite cool, infact the case feels cold to my hand, wife also said she couldn't feel any warm spots either.. so these incidents of overheating being reported is certainly not common to all of them.
Perhaps if one did turn the brightness to maximum, it may get warmer.. no idea not tried it.. why would I, as it would be extremely bright and likely unwatchable.
Thankfully all seems good so far, no light bleed at all, no bad pixels, good white balance, and definately no overheating... but better not tempt fate ;-) as it's most unusual indeed for me to get a 'good one' of anything I buy...lol