Here's a wrapup of some of the interesting things I heard about the overclocking capabilities of Intel's Nehalem chip:
Intel Turbo mode will boost the performance of single-threaded applications on all Nehalem processors. The chip will automatically put cores into standby mode and overclock one of the cores to maximize single-threaded performance. The Nehalem chip can deactive three of the four cores and overclock one core from 2.8GHz to 2.93GHz in just microseconds.
The Turbo Mode will operate in steps of 133MHz until the temperature gets too hot. One of the cool things about this is that better cooling will likely result in better performance, even for people who don't manually overclock their Nehalem system.
The Core i7 Extreme chips have no limits while the mainstream versions will have a maximum Turbo Mode of only two steps (266MHz).
Enthusiasts with a Core i7 Extreme will be able to specify how much heat their cooling solution can handle. If you have a liquid cooling solution that can handle 250W of heat you can adjust the thermal envelop value in the BIOS of a Core i7 Extreme system to 250W and the processor will then automatically discover how high it can overclock while staying below the specified boundary.