Personally I think NVidia are doing what is best by keeping the drivers closed source ("Oh my gosh! Sacralege! I hear you cry! :-)
Well if you think about it
1) NVidia own the patents/designs etc for their products, why should they reveal how they work ?
2) NVidia employ the people who designed the hardware and software so they've got all the expertise and should be able to produce the best software.
3) Open Source drivers are open to malicious tampering ... I'm quite sure you can hunt through google and find various references to backdoors being coded into various "free" programs.
4) NVidia will probably stick to a design methodolgy .. whereas open source developers prefer the hackit and postit method (from the Bodgitt & Skarper institute of learning)
Just my opinion :-)