How do you discover good/interesting questions quickly and efficiently to answer?
RSS feeds in conjunction with Notifixlite to get IM notifications on feed updates. I usually subscribe to the tag feeds of feeds I like, care about (like RSS :D)
I tend to pick categories that I have the most experience in and seek out the newest questions there. I like to take my time answering, and even then I go back and revise my answer on an average of 3 times just because I want it to be a good answer.
I'm not always the fastest to answer, but that's not what SO is about. It is about providing the best answer.
The main thing I've done is mark lots of tags as ignored, and hide questions with ignored tags.
I use StackGuru to store my preferred tags and have the questions delivered to my IM soon as they get posted.
I often use google to add references to further documentation.