This discussion has been taking place in this mailing list thread (and then carried on over to dri-devel) for the past few days. Brought up are how to expose power management options to the user (e.g. by sysfs or procfs), what sort of power management scaling algorithm to utilize, and basically how to handle this entire process.
Power management support for NVIDIA graphics cards in the Nouveau driver is not expected until the Linux 2.6.34 kernel or later, but it's certainly a matter of interest to many. The open-source ATI developers have also been working on their in-kernel DRM power management support too.