I too have heard CS5 uses CUDA, that could be a nice feature if you use that program a lot.
As far as gaming goes, both AMD and Nvidia have nice options. Nvidia has PhysX for games with GPU accelerated PhysX support. There are about 20 of those.
AMD's new cards have better AA options. SSAA isn't usable in a lot of games, but when you can use it, it really smooths things out better than other forms of AA. MLAA is also useful on games that don't normally offer AA.
I generally recommend a single powerful card over two lesser cards. While 2x 460's would definitely out perform the 6950/70, it comes with SLI baggage. Not all games support SLI (most do), sometimes they cause glitches (weird effects and/or stuttering), noisier (although 460's aren't bad I hear), and doesn't work in windowed mode. For me, I have 4 games which I don't gain benefit or have to turn off SLI to play.
So if it were me, and I used CS5 a lot, I'd look at the 570 rather than 2x 460's.