"However even with a dedicated socket, graphic card memory would still need to be soldered onto the board. The narrow tolerances of GPU memory would not allow for a DIMM-like solution. ATI's newest R520 GPU already advertises support for a wide range of memory products, including memory that has not even been announced yet."
Anandtech
View at TechPowerUp Main Site
Anandtech
View at TechPowerUp Main Site