Speaking as an nVidia fanboy, I think that ATi are going to release not only competitive cards this time around, but cards which in a fair few titles (arguably AAA Titles) ATi will have the performance Crown (and this is without even considering their MultiGPU Solution...which is bound to be epic).
My reason for this prediction is that for years ever since the ATi Radeon 8500 ATi has dabbled with Hardware Tessellation Technology...it's not until now that it really is going to take off, I think ATi's hard work and effort in this area will pay off in dividends.
The only area I can see nVidia beating ATi would be in games that use Hardware Physics (DirectX Compute, Physx, OpenCL et al ), this I can see being ATi's only flaw as nVidia have the edge here and have been making positive noises, ATi on the other hand have decided to wrap OpenCL to their AMD processor division....does make you wonder whether the ATi GPU's do not excel here.
I am looking forward to seeing the reviews... who knows I might even decide NOT to get a GT300, but instead go for a Radeon 5870!
John