Nordic Hardware has an update about memory overclocking on Intel's upcoming Nehalem platform. The site says Nehalem will officially support only DDR3-800 and DDR3-1066 memory, but there's a strong buzz that DDR3-1333 might be supported too.
The site writes memory overclocking will be harder on Nehalem as the memory and processor internals run at a synchronized voltage. There were some rumours this summer that running your memory at 1.65V would fry your Core i7 Nehalem processor, but according to Nordic Hardware that's too pessimistic. Rumour has it that it will be safe to go up to 1.7V but voltages higher than that may harm your processor:
Previous reports have stated that anything above 1.65V would fry a Nehalem processor and it would certainly be hard to get any of today's DDR3 memory modules to any kind of decent speeds at this voltage. But, these stories are exaggerated, but the fact remains that Nehalem processors are not going to like voltages above 1.7V.
You have to put it through some extreme handling for it to give up right away, but if you feed the memory with voltages above 1.8V, the processor could start degrading and finally cease to work. According to the information we've received you need to hit close to 2.0V to kill a Nehalem processor.
Also interesting is that memory timings will barely matter on the Nehalem platforms, low memory timings will improve your scores in memory benchmarks but the performance boost in real-world applications will be very tiny.
Nordic Hardware suggests the Core i7 will create a new DDR3 memory market segment with high-frequency modules at low voltages and loose timings. More info over here.