Well, DDR 3 should start from 1066MHz but it will also have 1333MHz modules available at launch. This is what Intel next generation chipset wants from the memory, you need to match the FSB and memory to get the most out of it.
The best thing about DDR3 is that it can do 1066MHz at 1.5 V and 1333 should work at similar voltage as well. AMD already said that it stays loyal to DDR 2 only, at least till the end of this year. DDR 3 is of course likely to end up more expensive at least at the beginning but the price will drop eventually, just give it some time.
Intel is committed to start the migration to DDR 3 this year, in Q2 with its new G33 chipset and P35 of course. µ