I've written and uploaded a simple free app to the play store, which allows someone to create a selection of gestures, and then to draw and see how well they get matched (or indeed, if the right ones even get matched).
In an ideal world, I'd be able to use this to author things like the Google maps pinch to scale in and out, or swipes to go from one page to the next. Unfortunately, while simple letter shapes like N, Z, C, W and more match perfectly fine, the functional gestures like pinch to scale and swipe to switch get confused and don't seem to reliably distinguish between the direction of the actual gesture.
Hopefully I'll get feedback from the mailing list, and it'll be something I am doing wrong. Otherwise there's a load more work in my future to use the Android Java-level gestures.