To help you in that mission, we’re introducing Android Design: the place to learn about principles, building blocks, and patterns for creating world-class Android user interfaces. Whether you’re a UI professional or a developer playing that role, these docs show you how to make good design decisions, big and small.
Probably the biggest thing that annoys me about the Android ecosystem is the general inconsistency of apps. The navigation is always different with apps along with the look and feel. It's amazing that it took this long to come out with "design guidelines":http://android-developers.blogspot.com/2012/01/introducing-android-design-site.html for developers to follow. I know that when I was exploring Android it was frustrating that there was nothing like this available at the time.
Contrast this Apple and their "iOS Human Interface Guidelines":http://developer.apple.com/library/ios/#documentation/UserExperience/Conceptual/MobileHIG/Introduction/Introduction.html which was one of the first iOS developer documents I read. The iOS App Store was initially released on July 10, 2008 and according to the "revision history":http://developer.apple.com/library/ios/#documentation/UserExperience/Conceptual/MobileHIG/RevisionHistory.html#//apple_ref/doc/uid/TP40006556-CH2-SW1, the guide was written back in June 27, 2008.
If you asked any random iOS developer they could easily tell you certain facts such as the exact pixel length and width of an iPhone/iPad or the exact pixel height of a default table cell. It's this type of consistency and attention to detail which makes iOS applications instantly accessible and one step closer to greatness.