The stylus keyboard input method. Not because it needs fixing in Diablo (it's as close to perfect as it can be IMHO), but so that it can be ported to Fremantle (where the available input methods leave much to be desired, all covered in other threads) and possibly Mer. Use cases: much more usable command line work, editing code (or even just discussing commands and code in chat/email), any input use case that involves alternating between numbers and alphabetic characters a lot, multilingual input. (Once the N900 launch dust settles down, it'd be nice of Nokia to clear the backlog in http://wiki.maemo.org/Why_the_closed_packages - last answer over 10 months ago).