Google knol was criticized for the possibility of potential Plagiarism.
Now, it seems Google is taking solid steps for preventing Plagiarism. Google is allowing the users to complaint about any Plagiarism. You can see the more details at http://www.google.com/dmca_knol.html
Google is showing a poll in the knols which got any complaints to decide whether the complaint was valid.
You can refer this knol for more details.