In Riposte for App.net, you can change brightness with three-finger swipes up and down. Note that this doesn’t change brightness in just Riposte, you’re adjusting your device’s overall brightness setting. It seems strange, but I’ve found this to be faster and more convenient than digging into Settings just to change brightness.
I agree with the Riposte devs—I’d love to see Apple add some convenient system-wide gestures like this in iOS 7.