A group of authors are allowed to create an article, or a Knol, this group then moderates the article by acting as gatekeeper to any changes made by other users outside the creator group. This imparts a sense of ownership to the author group. More than one knol can be created on a subject. Each knol can be rated by a group of users; rating which would perhaps be leveraged to search and sift through the numerous knols sure to be created on a topic.On the surface, this seems like a good system: on the one hand you have accountability, and on the other, incentive attached to that accountability. A good article would be a popular article, and a popular article would be more likely to get AD revenue. The circle is of a positive feedback. It would be an interesting social experiment to see which one of the two: Wikipedia -- which encourages social contribution to further group knowledge, or Knol -- which throws in a dash of capitalism to the mix; will be embraced by the larger community. Of course, there is no reason why both could not co-exist, perhaps Google could link out to related Wikipedia articles and vice-versa.

As an aside: as of the time of writing this -- there doesn't seem to be a Knol for Wikipedia, whereas there is a Wikipedia entry for Knol. Yes, we know, early days for Knol but still worth a chuckle.