The Linux hybrid graphics patch known as "vga_switcheroo" is now on its sixth revision. The fifth iteration of the graphics switcheroo migrated some of the ATPX handling in the xf86-video-ati driver and the sixth does some preparatory work for hooking in Nouveau support so that NVIDIA graphics processors can be switched on and off. The latest version of this patch can be viewed here.
Airlie has also written a second patch that adds delayed GPU switching. Rather than needing to shutdown the X Server, change run-levels, write to /sys/kernel/debug/vgaswitcheroo/switch, and change back, delayed switching makes the process of switching between GPUs a lot easier. This patch still allows immediate graphics switching to a discrete GPU and an integrated graphics processor, but the delayed switching basically postpones the switch until the X.Org Server is restarted. In other words, it's a lot cleaner to integrate that as soon as you log-out and GDM restarts itself, the delayed switch can occur automatically.
Now we just need the Nouveau driver properly hooked in for NVIDIA graphics card support, GDM integration, and then for the kernel patches to be merged into the mainline kernel. Judging by the pace at which Airlie is attacking this hybrid graphics support, perhaps it will be done tomorrow?