We need a driver which:
1) doesn't starve the GPU by doing too much CPU work
2) doesn't synchronize the CPU with the GPU, so that the two can operate asynchronously
3) takes advantage of every hardware feature which improves performance
FYI, I was told by some NVIDIA guy face-to-face a few years ago that their Vista GPU drivers had 20 million lines of code. The entire Linux kernel has only 14.3M.