Louie Mantia imagines what iOS 7 may look like from the Settings app. I love his use of Avenir, a font that I have absolutely fallen in love with. I use it in any app I can (e.g., Day One and Twitterrific 5).
Louie makes a lot of other smart decisions, and I think I would love it if iOS got a bit of a makeoverin this style.
Some related reading would be Chairman Gruber's little birdies.