A little demo of a script I did to enable autocomplete for twitter replies.
I wasn't happy with the existing options, they were either bloated or unreliable, so I hacked up a simple option that complete as you type and cycle throug options when you press Esc, Textmate-style. When the prediction is the name you look for you can just press Tab or the Right Arrow to continue.
Installation at http://fabricio.org/greasemonkey/twitter.simple.autocomplete.user.js
Source at http://github.com/fczuardi/autocompletter/tree/master