DDR3 has architectural improvements over DDR2 which means even at the same frequency it should offer similar if not better performance (even given its higher latencies). As DDR3 matures the latencies at 1066 should drop without the need for any increased voltage so there will still be headroom for a bit better performance has the platform ages.
Also, memory bandwidth is a function of both frequency and channels. The memory controller on the high end Nehalems is triple channel so theoretically it should be to give a 50% improvement in bandwidth over Core 2 Duo (Yeah right... not going to happen... but it should be faster).
Same performance in most cases, if memory can be read linear it is faster, if it has to jump around, it's actually slower.
It's more bandwidth, but due to the fact, the third channel can't be interleaved, it does not really matter if two or three channels.
With prices skyhigh for DDR3, it's quite frankly a expensive choice without substantial benefit.
But as we know, Intel and M$ are doing much to get the industry some money, but in case of M$ it does now backfire (Vista Capable Class Action)... so both try to maximize profits, but we have the choice not to let them
As stated in my article, if you don't need the power, there is no reason to switch your system...