You've heard of rap battles... now how about poetry battlez... it's geeky little brother.
Take the same topic as someone else, and write something original on it, to see who takes the crown... If we got enough people, we could have like a knockout tournament decided by the highest voted of the two poems per topic.
For each reply, leave a branch for someone to challenge you at the same topic, as well as inventing 1 or 2 new topics.
Hope that makes sense..