Graphics RAM is becoming more interesting, at the moment. ATI is clearly playing it both ways, with this new announcement increasing the amount of on-board memory and its HyperMemory technology decreasing it. It's interesting to consider why anyone would need 512MB memory right now, and the answer is to run at stupidly high resolutions or to run with lots of anti-aliasing. There is also the question of graphics memory moving to next-generation XDR technology, from RAMBUS.
There is a growing amount of evidence, as well as some talks, that the next ATI part will not contain more pipes or higher clocks -- but rather that it is getting a huge memory bump.