gfxCardStatus allows users to control which graphics card is enabled -- integrated or discrete -- on MacBook Pro models with multiple graphics cards. By more precisely controlling when each graphics card is enabled, users can improve system performance or battery life. gfxCardStatus is a menu bar application for OS X that allows MacBook Pro owners to view which GPU is in use at a glance, and switch between them on-demand.
Ars Technica has much more, including the fact that the Retina MacBook Pro can be pushed to nearly 10 hours of battery life with some minor battery saving techniques:
I was consistently able to get between 8 and 8.5 hours of continuous use from the Retina MacBook Pro when running integrated graphics only. Turning down screen brightness to just two "dots," a technique I often use to maximize battery life when using a MacBook Air during conferences, caused OS X to report potential battery life as high as 10 hours. I simply didn't have the stamina to test that claim, but I did make one nine-hour run with OS X reporting a nine percent remaining battery capacity.
gfxCardStatus is a free download from creator Cody Krieger's website.