The points scheme is quite simple. You get one point for every comment you post and 10 points for every story you post. In the near future, you'll get three points for rating a story (that functionality hasn't been implemeneted yet). So the more you read, and the more you contribute, the more points you'll get -- and the more your fellow PoopReporters will pay attention when you say something.
So why does The Shit Volcano have so many points? Because she hasn't posted many stories, but she's commented the hell out of the stories on this site. And Poonurse? She hasn't made too many comments, but she published a ton of articles in the PoopReport medical database [1].
And why do I have so many points? Maybe it's because I've commented the hell out of the site AND posted a ton of stories. Or maybe I cheated and gave myself 3,000 points to appease my giant ego. One of the two, that's for sure.
Also, in the near future, everyone will have their points listed next to their names -- not just the people in that sidebar.
Update 9/22/05: Now you can see users ranked by points [2]! That's a good step... more to come!
Update 2/15/06: Now good and bad comments are rewarded and punished [3]!