I'd like to see SO implement user based tags like delicious.
For example, if no one is answering my question, but I know Scott Hanselman would know the answer I could tag my question "for:shanselman".
Then when Scott logs in he would have a list of questions directed at him to answer.
I acctually think that if a user is sent a direct question and answers it, this should be worth slightly more reputation points, because you are proving your "real life reputation" in the system.
This could also create bon-a-fide experts so that a question that hasn't been answered in a while could prompt the asker: "You should send this to XYZ" where XYZ is a leader in the tag category for the question.
I think this system also adds more merit to blog flair, because your blog flair could have a link to "ask me a question" which would all get funneled through the SO system.