I guess it depends on how you define "lead"... There are a number of different segments to consider. These are my predictions:
DX9 Performance crown: NVIDIA. I think they are more focused on making a high performing DX9 card that is also DX10 compatible, and this will show in DX9 performance.
DX10 Performance crown: Tough to say overall, but I think ATI is going to have it. They worked with MS for the Xbox 360 chip, plus they just seem to be more focused in this direction then NVIDIA. Hopefully, the acquisition won't interfere with R&D at ATI too much.
Multi card/gpu solutions: NVIDIA. Dual card SLI will only get better, but I don't see any development for G80 based Quad-SLI in the near future if the heat/power rumors are true. ATI/AMD will still be playing catch-up with a new dongleless Crossfire, user editable/creatable profiles, and a chipset solution that doesn't rely on a ULI SB. The Crossfire capability of the 975X chipset and Conroe will help increase the popularity of Crossfire in the meantime though.
Image Quality: ATI will continue to dominate this as they have for the past few years, as I feel that IQ is overall a higher priority to ATI than NVIDIA. However, I think that NVIDIA will adopt angle independent AF and HDR+AA. Perhaps one (or both) will be able to implement high levels of AA (+8x) with a single card.
...just my 2, or 3, or 4 cents...