Double post, I know, I'm naughty. :P
nVidia can do 64x Anti-Aliasing with GTX295 Quad-SLI.
That's nuts, in an extremely awesome way. Not really a feasible proposition for most of us widescreeners, as we tend to play at rather high resolutions... but for those with lower res screens, it'll mean that buying something like that wouldn't be a total waste of GPU power.
(Of course, if anyone spent $1000 on GPUs, but then didn't buy at least a 24" screen... they're really just spending money for the sake of saying 'I've got quad-SLI!' ;))
I'll admit (in my obvious bias against nVidia) that I'd like to get a GTX295. It's not really until 2560x1600 that the memory limitations (wrt size/bandwidth) start to show so it'd be ideal for 1920x1200. It's all down to price... if it's £50 or more cheaper than the 4870X2, I'll probably try to get one. If not... I'll wait a bit longer.