Wow... this is, almost _exactly_ my final project for a class I'm in. I have to do some pretty serious stuff as far as the actual filtering goes, but the frontend is exactly what I've been working on down to the plugins (Redis/Sinatra/Haml/Jquery). This is amazing timing.

* Note: No, I'm not using this to cheat, I'm using it as a reference since my implementation is very different, and the actual filtering is what I'm being graded on. ;)

Glad I was able to provide a good starting point. :) It's fun technology to play with, and TweetStream makes the actual filtering amazingly easy. Good luck with your project!