This has been an issue ever since they went unibody. A single, solid block of aluminum in direct contact with heat generating components. It's hard to believe they didn't intend the unibodies to act as heatsinks. Hasn't hurt their popularity at all, though.
I had a first generation MBP Intel back in 2006 , Core Duo, before the unibodies came out. Now THAT one was hot - I had to keep the fans cranked through software all the time or it would randomly shutdown from overheating. Apparently it was a misapplication of thermal paste in the manufacturing process.
Other unibodies have been okay, the retina MBP being the best so far I find at even heat dissipation.
I also had a pre-unibody core duo. Mine was a 17 inch, though. Guess mine had all its thermal paste in the right place. :) It got hot enough to be uncomfortable, but not hot enough to burn.
