Robert Scoble started a good discussion in the last few days with both economy-business model points and technical-cooperation-definition points. Look at this, or this to catch up on it.
I think there are three things here:
  1. what would you pay to keep reading and using (advertising-earning, self-sustaining blogs)
  2. what you share for the value of sharing and getting back ideas
  3. "look-at-me-mom" blogs, successor to the tombstone web sites of 1997 or so

The feelgood one, so the popular one, is number two, best commented by Scoble here. His first stab at it was really looking at number one.