Digit-Life posted a comparison review between DDR2-800 and DDR3-1333 memory. Here's a taster:

So, we're going to compare performance of two processors in combinations with different memory modules: standard DDR2-800 and higher clocked DDR3-1333. The Core 2 Extreme QX9650 processor (1333 MHz FSB) will be tested on one and the same motherboard that supports both memory types (Foxconn X38A). And the Core 2 Extreme QX9770 processor with the 1600 MHz FSB will be tried on two different motherboards. These motherboards come from the same manufacturer, the same series, and they are practically identical, except for their memory support (DDR2 and DDR3).

There is no miracle again: faster memory yields 1% performance gain on one of the fastest processors with the 1333�MHz FSB, while the only processor for the 1600�MHz bus gains 2% from it. As always, faster memory appears much earlier than we really need it. But let's not act as ignorant users, who shout about being cheated. There is no cheating here. Look at results and draw your conclusions. Sooner or later, we'll have processors that will be able to use the full potential of DDR3-1333. It would have been naive to think otherwise. It will just happen later, that's all.