Athlon 64 for Quiet Power :: SilentPCReview.com. A good review of the power consumption differences. Has a great slide on actual power consumption of CPUs:
!http://www.silentpcreview.com/files/images/column/seti.png!:http://www.silentpcreview.com/article169-page3.html
Basically shows that the new Intel Prescotts and Northwoods really burn up lots of power. Quite a reverse from the Athlon XP which was way hot and the original Pentium 4s.