David Airlie published this week patches to provide Optimus dynamic power off for the Nouveau open-source NVIDIA driver. This work requires changes to VGA Switcheroo, the Nouveau DRM, and the HDA_Intel audio driver for turning off power to the secondary GPU in Optimus laptops. This obviously saves a lot of power not having to keep the second GPU powered on when it's not even being used at the moment for rendering.
If the patches work well, the secondary GPU should then power back up when it's needed, whether it means when running commands like lspci or using DRI_PRIME for offloaded rendering. No manual intervention on the behalf of the end-user is required.
Aside from NVIDIA Optimus laptops, this work is also intended to help MUX-less AMD PowerXpress laptops too, but right now just the Nouveau driver is implemented. Sadly though this isn't related to any improvements with regard to dynamic re-clocking for better allowing NVIDIA GPUs controlled by the Nouveau driver to better re-clock dynamically to their highest performance states.
The current patches for this Nouveau Optimus dynamic power off support can be found on the dri-devel mailing list and will hopefully be merged into an upcoming Linux kernel release, at the earliest it would be the Linux 3.12 kernel.