The new NVIDIA System Tools 6.03 (previously known as ntune) allows you to overclock the now MacBook via BootCamp, and more precisely the GeForce 9400M. Without pushing the hardware too far, I reached 2.3 GHz for the CPU and 580 MHz for the GF 9400M chipset (from 470 MHz default).If you want to try it yourself, you can get the NVidia tools at the following address: http://www.nvidia.com/object/nvidia_system_tools_6.03.html
With some 3D demanding games such as Simulator X or GTA IV, the computer can freeze if you overclock the GF 9400M to 580 MHz, however, bringing it down to 550 MHz fix this freezing problem. You can also leave the GF 9400M at 580 MHz, but bring the CPU down to 2.0 GHz. This freezing problem might be linked to the RAM usage/frequency/syncing.
As usual with overclocking, be careful, and do not forget that a mobile computer is usually a compromise between performances, heat release and battery lifetime. If the overclocking might be useful when you a directly connected to power, on a remote usage it will definitely affect battery lifetime, without mentioning the potential effect of components.
