They do, but for a game like Left 4 Dead I'm probably going to be looking at the neighborhood of ~40 FPS average (4xAA, 16xAF) for the 9800 GT rather than ~60 FPS for the 4850, which is right around the sweet spot.
C'est la vie. 40 FPS is still playable, I guess, and I'll be looking to buy a new machine (Nehalem-based) within a year anyway. It'll do. (Plus the card comes with Call of Duty 4, so that's a bonus.)
I'm hoping it'll get here tomorrow afternoon. If so, I'd be up for some gaming tomorrow afternoon or over the weekend!