raw memory bandwidth.
but memory holds textures, textures are a collection of colors, and colors are compressable by algorithms and (according to nvidia) they say they can really get that 1ghz DDR2 working for them with up to 32GB theoretically (its all theoretical) but thats definitely saying 'drivers can make this puppy sing'
maybe worth the wait.
i gotta tell you my last card, nv20 ( the Geforce3, bought it for 400$ the day it released. amidst alot of critisizm from Geforce2Ultra owners that schooled it in the benchmarks) got me two years of really nice gameplay. i get almost double my first scores in 3dmark2001 almost two years later! such an example of scale-ability at its best. it played BF1942 at 1024x768 with 4xAA (always no AF of course) at very smooth framerates.
so we got an interesting year ahead of us.