In kernels >=34 included support for switchable graphics, on this subject, it is necessary to Google vga_switcheroo. Enough to have two one-line script to switch video and do not forget to restart the X server.
Overall are the owner of a laptop with 2 cards: one Intel, the second is ati 4650. The latest versions of Linux distributions start immediately. Yes, will have to abandon drivers from the vendor as is the case with AMD, and in the case of Nvidia.
About Nvidia, as I remember the nouveau developers have pledged their support for switchable graphics, I don't know how they have it now.