lol! I can't find a nice doc that describes limitations, but we can do multi-touch for sure. One minor issue with single-finger 'up' and 'down' is that they will not work at all when the screen is setup to scroll vertically. Which it needs to be to satisfy multiple device resolutions. I have implemented the physical buttons as a straight swipe to the right or left and then a /\ shape for up and \/ for down. Your numbers idea is great as usual, with the minor issue of drawing the 1. It cannot be a simple straight vertical line (see above), but could be drawn like this:



The rest of the the numbers are easy
The nice thing about gestures in Android is that you I can build numerous different attempts at a gesture and name it the same as previous iterations which increases the fuzziness For example, I could create 10 different gestures of the number 8 to increase the app's likelihood of a match when users swipe an '8'. All of my gestures would be slightly different just by virtue of a dumb finger against a digitizer

I am not sure about vertical multi-touch limitations and there may well be none. So that would be nicely solved before it became a problem.

Tomorrow, I'm getting on a plane and flying to a foreign beach for a week so I'll be back at this at that time. Fiesta!

Cheers