It seems there is a problem with the new macbook, the cooler doesn't exactly know when to turn on and to turn off.
http://video.google.com/videoplay?docid=-4490733167064230159

It's exactly the same with my asus cheap ass sempron laptop, and i am really thinking of selling that one to go to a macbook. Main reason is the fan, i get tired of it. But now seeing this..

edit:
http://www.ocf.berkeley.edu/~chrispl/Moo.m4a

another mooo

some of the macbooks come with a bit of plastic stuck over the vent. take it away and the laptop can breathe properly - this is meant to be linked to this.

btw my mbp mooed before they updated the firmware. it doesn't any more!

my sister just had to exchange her macbook pro cause it kept shutting down all the time.