Its been made clear not too long ago that ATI would be the first to implement GDDR4 memory on their next GFX monster, the X1950XTX. Although these cards are yet to be released / shipped in volume, there's already talk of GDDR5 reaching partners by mid 2007!
HKEPC have the full scoop.
DRAMeXchange, a research company in the memory market, released a trend estimation report on graphic memory (GDDR). It pointed out that game console products would push forward the demand for GDDR in 2006 Q4, and the wave would be followed by the release of Windows Vista in 2007 Q1. As there will be an increased demand for GDDR memory in notebooks and game consoles, DRAM manufacturers plan to raise the production of GDDR chips to fulfill the demand in the coming 2 quarters.