The key principle behind Knol is authorship. Every knol will have an author (or group of authors) who put their name behind their content. It's their knol, their voice, their opinion. We expect that there will be multiple knols on the same subject, and we think that is good.
With Knol, we are introducing a new method for authors to work together that we call "moderated collaboration." With this feature, any reader can make suggested edits to a knol which the author may then choose to accept, reject, or modify before these contributions become visible to the public. This allows authors to accept suggestions from everyone in the world while remaining in control of their content. After all, their name is associated with it!
The items on the home page seem to show a bias towards medical issues, with articles on Carpal tunnel syndrome, Chronic stomach pain and Thoracic outlet syndrome. However their are also links to more mundane things, such as how to install a kitchen tap. The general idea seems to be that all is grist to the Knol mill.
Articles are signed and may be edited - but any edits have to be approved by the author(s). The obvious comparison is with Wikipedia and Citizendium - Knol appears to be more like the latter than the former and I imagine we may see the same persons contributing to all three. Of the three, however, Citizendium seems to have the better editorial control - which is why my own developing article on Information Management is there.