I'm getting a 128Mb because the guys who I'm getting the rest of my new toys off went out of stock of the 64Mb and my wife didn't want to have to listen to me whine about it
I justify it thus:
* The Gf4s and Radeon 8500s are all coming with 128mb now, 128mb will keep the card usable longer.
* AGP 8x is coming, bigger games with more textures with it probably, a 64Mb card with AGP 4x might get badly bogged down, a 128Mb card will have to load textures less often, and might just cope.
* It's cool to have 128Mb on your graphics card so you can make fun of the friends you know who only have 128Mb or less in their whole system
* It keeps the memory manufacturers in business, can you imagine, the poor dears have being having a tough time lately, awwww bless