The NVIDIA G80 has been taped out a couple of weeks ago and The Inquirer also learned the chip is fully DirectX 10 and Shader Model 4.0 capable but it doesn't feature a unified shader architecture.
And the firm decided it doesn't need a unified Shader for its upcoming G80 chipset. Instead, it decided that you will be fine with twice as many pixel Shader numbers as geometry and vertex Shaders.
AS we understand it, if a Nvidia DX10 chip ends up with 32 pixel-Shaders, the same chip will have 16 Shaders that will be able to process geometry instancing or the vertex information.
ATI's R600 and its unified Shaders work a bit differently. Let's assume that ATI hardware has 64 unified Shaders. This means that ATI can process 64 pixel lines only per clock. That may be in the proportions: 50 pixel, 14 vertex and geometry lines per clock, or 40 vertex, 10 pixel and 14 geometry information per clock. Any ratio that adds up to 64 will do. I hope you get this maths.