It seems to me that most tags will be just like subreddits, and they will just be the same posts reposted again and again.
I really like Hubski so far, and I don't want to to become boring.
Edit: How do you make multiple tags?
Well, how bad do you think that repetitive questions are? People change, so answers will differ with each instance of the question. Also, it might be that the question will not reach you because of how Hubski works. If a question is repetitive it might not be shared. Things like what mhr suggested are things which the design of Hubski might provide. About tags: You as the original poster set the main tag. Other users can suggest the other tag. The most popular suggested tag will be displayed.
it'd be cool if there was some sort of feature that detected if a post was unoriginal based on the title (after all, if a question is similar to another question, it must have some level of similar words), and notified the poster that the post was unoriginal.
It wouldn't necessarily prevent the question from being posted, it would just tell the poster that the question may be unoriginal and show some previous questions that had been posted that had the same keywords. If the poster has hubski's best interests in mind, then he/she would do more research and check whether they were in fact reposting a question. If they don't care whether they were reposting, then it's a lost cause anyway.