Paranoid, and others discussing the AF thing, I should clarify that indeed the smoother AF levels with ATi don't exist across the board. Sometimes it a driver issue, sometimes it's a game issue. I don't want to sound like a fanboy here. AF looks much better in UT2k3, but I get that hard distinction in Planetside. But *overall* I've experienced cleaner AF and seen benchmark screenshots of cleaner AF and AA with the recent ATi cards.
Anandtech had a review a while back that compared these elements between the top two cards, and ATi came out on top--however, nVidia said that those screenshots weren't representative of final output because some additional things are done to the image after it leaves the buffer. They didn't specify, so it could be some proprietary algorithm or BS. Whatever the case, both high end cards will give you a great gaming experience, and I wouldn't be surprised at all if the NV40 polished up the AF to be on par or better than what ATi is doing.
Also, as it stands *right now,* nVidia's current lineup drops of significantly in AA performance after 4x. Take a look at Hardocp's reviews, or any other review that graphs all AA modes, and you'll see ATi goes on a relatively gentle downward slope, while nVidia drops off a cliff at 8xAA. It's a little odd, and disappointing since the high-end nVidia cards are the only ones that do 8xAA, IIRC.
That said, I'm looking forward to seeing the NV40 kicking some ass. All I'm interested in is the best bang for the buck, and that requires at least two companies duking it out neck and neck in order to keep prices out of the stratosphere and features on the cutting edge.