MacBooks have at least a 1.83Ghz Core Duo processor. No one expects them to feel like an ice cube when running. However, it was revealed in this post at Apple's official messageboards by Jean Cyril that Apple had been a little excited with the application of thermal grease to the Core Duo, ATI GPU, and northbridge on the new MacBook logic boards, and that this is most likely the reason why they're getting to bloody hot.

According to Interrupting Moss from Somethingawful, here, it takes a slight misapplication of thermal grease on a MacBook Pro to make the temperatures skyrocket. When he took the back off his MacBook Pro he found that was just what the assembly teams at Apple had done. On the forums he shows before and after pictures and measures the temperature gauges to prove it. He scrapped off Apple's attempt at thermal greasing and reapplied the paste correctly. Now his laptop does not get as hot as it used too. Moss said that most people think that their new Apple's are supposed to get a bit warm, but there was no way they needed to get THAT warm.

Warranty note: This may or may not void your warranty. The only "seal" you have to break is on the left fan, a piece of tape you have to cut. I don't see how this could indicate you yourself messed with it, though; an Apple tech could have done that at some point (especially if you have a refurb like I do). So whatever. Don't fuck up.

WTF Apple... I can't believe that a company that has made such great notebooks over the past few years can fuck up something as elementary as the proper amount of paste.