Nvidia to switch to monthly driver update schedule
 

Some background info on Vista driver development and what's holding them back:

"One difference between developing SLI for Windows XP was drastically different than it was for Windows Vista is that the NVIDIA hardware and driver could basically work together to make SLI function without letting the OS know what was going on. This put the entire software stack in NVIDIA’s hand, making it easier to find patches and loop holes to get SLI performance to scale well. Vista’s dramatically changed graphics driver model will no longer turn a blind eye though, and because of it, the amount of driver development time has increased.

http://www.pcper.com/article.php?aid=357

Very interesting article. I have the feeling "optimized" drivers for Vista will be a long ways away now however...