FWIW I have 2 machines running the GeForce 8600GT's w/512mb and have never had a problem with them.
Michael, I don't have links to back this up, but last summer I was looking for a better card for a Vista system, the GeForce blew the doors off of much more expensive Quadro's. This was due to the GeForce's being optimized for DirectX10, where the Quadro's were optimized for OpenGL.