Google's doing a lot to bolster its Android developers guide at the moment, with fresh design tips and then a new section on accessibility arriving shortly after. The latter provides a bunch of suggestions on things like minimum button size (48dp or around 9mm), and also explains how to make use of free components like TalkBack, which gives a spoken description of an app's UI, and Eyes-Free Keyboard, which many users find easier than regular touch-to-click.
2DayBlog.com, Android devs: if you can't use your app with your eyes closed, open them and read this
