gfxCardStatus is a great tool to help you control which GPU your new Retina MacBook Pro will use. This will also work on other Macs that have a hybird GPU
For Example, if you are running on battery and are browsing the internet with Chrome or Firefox, the system will switch to the Discrete GPU instead of the Integrated GPU which uses less power. With this tool you can force the system to stay on the Integrated GPU.
Safari seems to work with MacBooks with the auto switching GPU as it does not force the system to switch to Discrete GPU unless you really need it, For example if you are which Netflik then it will use the Discrete GPU.
When this app is opened it stays in the top right menu area and you can set this app to open when the system starts up.
It let you know which GPU is being used, and what application is using the Discrete GPU and it can use the Growl notification system to display messages. It also works great with Mac OS X Mountain Lion and OS X Maverick.
You can get gfxCardStatu from http://codykrieger.com/gfxCardStatus