AnandTech investigates the new 65nm Xbox 360 consoles:
Microsoft just recently dropped the price of its Xbox 360 and around the same time, rumors crept up about a quiet introduction of 65nm CPUs into the bill of materials. The original Xbox 360 manufactured from 2005 up until August of this year all used 90nm chips; the CPU, GPU and eDRAM were all fabbed on a 90nm process, which was state of the art at the time. However, as you've undoubtedly noticed with Intel's recent move to 45nm, 90nm is more than dated now.
A move to 65nm would undoubtedly reduce power consumption, potentially make the console quieter and obviously make it cheaper to produce. With the Xbox 360 there's also another side effect that many surmised would result from a move to 65nm: increased reliability.
The reporter concludes the new 65nm Xbox 360 consoles use a lot less power. In idle the old 90nm Xbox 360 uses 149W while the new 65nm version consumes only 100W. While playing Halo 3 the old console uses 173W and the new 65nm console only 120W.