I love this site! I think you will notice a trend with people posting challenges on the message board. I think it would be awesome to have a "Challange" section in its own right. Where members can create a new challange and select the types of things that people will want to track if they join in on the challenge. This will make a simple grid where you can sort each member for each area of the challenge and see who is closest to being on top (at reaching the challange goals).
Typically when you add a bit of competition, people generate better results.
I have tons of ideas for how this section could work and would be happy to send you mock-ups. Let me know.. I was a UI developer for years...