This looks really neat. I'm put off by the python requirement, but this seems simple enough that I might try to put a C client together, or even something in my new language that I've been meaning to add networking libraries to..
This makes it hard to implement global @replies, therefore there’s no recommend way of handling those at the moment. You could just write "@<NICK>:" and hope that the person you had in mind follows you and feels concerned.
Maybe I’ll implement something which makes it easy for users to specify custom filters and/or highlights.