Depends on the game and quality settings. I can max out 1024 MB of VRAM at 1680x1050 with an overclocked GTX 460 before the GPU can't handle it in at least three games I own (using maximum in game settings). In other words, FPS is smooth up to the point it hits 1024 MB of VRAM used. Skyrim is the latest game to be like that for me.
Get the 2GB version if you can afford the extra $40 or whatever, especially if you plan to SLI someday. Don't gimp your multi-gpu setup with insufficient RAM.
I agree. BF3 multiplayer easily maxes out my 1gb vram on my gtx 460 at 1680 x 1050 w/ everything maxed out. If I was to buy a card today I'd buy a 2gb card. I don't want my vram to be my bottleneck.