I agree that 2GB is fine
but today on Battlefield 3 I hit 2212 GB Vram on Ultra and 4x MSAA :) (1440p)
Also Crysis 2 in DX11 mode with high res texture pack hits 2250ish GB Vram as well.
Keep in mind that in BF3, ultra with 4xMSAA my average fps was 40ish with a 670
In Crysis 2, my average fps was in mid 30s with a single 670
I would need an 670 SLI to run those games around 60fps.
YES 2GB cards are enough but if you can afford it, it would never hurt to get a 4GB card. It could pay off next year, Who knows.
Also kcuestag says that disabling windows aero reduces Vram usage. Keep that in mind as well