Check out the ELSE interface on Engadget, some really nice ideas for how a one-handed user interface could work, altough it needs a southpaw version:

http://www.engadget.com/2009/11/24/e...o-be-a-game-c/

I have no idea of how hard it would be to copy/port/create for N900, but it sure would be usable. Anyone else?