Dasher is text input informed by information theory. It's also trippy. David MacKay recently gave a talk in the Google TechTalks series. You can download a prototype at the official site. Plenty useful, but perhaps also a new metaphor for writing?
Dasher is a new way to input text on a Pilot or any computer without a keyboard. There's a version available for download to try out on your desktop, using your mouse. It really is quite freaky to use. The amazing thing is, it actually appears to work. After a couple of minutes experimenting, it's almost as fast as typing for a slow typist like myself.