From the 7 benchmarks from the front page, it pretty much boils down to two factors: what sort of color depth do you want (16 or 32), and how much are you willing to pay?
The GeForce 2 Ultra outperformed the GF3 at 16-bit color, but got spanked at 32-bit. And naturally the GF3 will be more expensive than then GF2U, but I'm not sure by how much. The GF2U was still pretty expensive last I looked, but I wouldn't doubt it's price will drop with the release of the GF3.