Looks pretty good, less power and less cost and better performance. Looks like the prices might not sky rocket either.

"GDDR4 will start working at the similar speeds of top GDDR3 chip but it will use less watts and will be easier and cheaper to produce. This memory should start around 800MHz efficiently 1600 MHz if not even higher. However GDDR4 will be different from GDDR3 as it requires some memory controller modifications so older cards should not be able to support it. The first chip that will be using this memory is Shader Model 4.0 NVIDIA chip known as G80."

Source: VR Zone