I've written an IRC bot that can notify channels when new questions with a certain tag are posted. However, currently I'm polling the URL #{APIURL}questions?pagesize=100&fromdate=#{@_lastQuestionsDate}&tagged=node.js&key=#{KEY} every minute.

I think that a streaming API would be better - easier to use, faster notifications and even less network traffic.
How about implementing one?
It could probably reuse the filter logic from the query API and apply it to all events.