http://mattgemmell.com/2013/06/12/ios-7/
http://blog.mengto.com/ios-7-transition-flat/
http://designmodo.com/flat-design-principles/
http://www.marco.org/2013/06/27/ios7-as-defense
http://whoo.ps/2013/05/12/flat-design-is-great-for-mediocre-designers-like-me