The bright flash of daylight color temperature when the MacBook Pro's switch graphics cards is the only downside* that I've experienced using f.lux. After you've been using it for a while it's painful to use a computer without it at night.

*for non color-critical work

If the automatic graphics card switch annoys you (it annoys me), you can disable it with this handy app: http://codykrieger.com/gfxCardStatus