Many forums have the ability to tag a post (often with multiple tags). This site does too, I see. What is the best way to prepopulate these tags? I know here users can add new ones after they get enough karma. That isn't so with some software. I have a very broad topic for my community, but obviously don't know the specifics of what will be discussed yet.

As a follow up, how can tags be maintained? I think it is a maintenance nightmare to keep these tags updated and relevant. I see tags becoming outdated or vague as the site grows and more niche discussions are more common. How does that get managed?