Regarding the Catalyst performance gains that were discovered in 3D Mark 2003 ATi has responded with the following:
The 1.9% performance gain comes from optimization of the 2 DX9 shaders (water & sky) in Game Test 4. We render the scene exactly as intended by Futuremark, in full-precision floating point. Our shaders are mathematically & functionally identical to Futuremark's & there are no visual artifacts; we simply shuffle instructions to take advantage of our architecture. These are exactly the sort of optimizations that work in games to improve frame rates without reducing image quality & as such, are a realistic approach to a benchmark intended to measure in-game performance. However, we recognize that these can be used by some people to call into question the legitimacy of benchmark results, & so we are removing them from our driver as soon as is physically possible. We expect them to be gone by the next release of CATALYST.

Meanwhile NVIDIA says the following regarding Futuremarks findings:
Since Nvidia is not part of the Futuremark beta program (a program which costs of hundreds of thousands of dollars to participate in), we do not get a chance to work with Futuremark on writing the shaders like we would with a real applications developer.

Draw your own conclusions to these reponses.