Some perspectives on Knol. An enthusiastic one from Ron Young: KNOL - a unit of knowledge from Google and less so from Dave Snowden: The reductionist knol and The controlling knol and from Danah Boyd : knol: content w/out context, collaboration, capital, or coruscation.
My opinion: I am in the Snowden and Boyd camp. Without any robust process to ensure the accuracy of the articles - the breadth of quality will vary from extremely good to total rubbish or articles published by people in order to promote themselves or their obscure point of view. And whilst, Wikipedia articles are alive - they are always being challenged and updated, Knol articles are pretty much dead once posted.
I understand Knol is different to Wikipedia. Wikipedia is an encyclopedia whilst Knol is a library of articles but it still does not make up for the lack of screening or quality control.
Take a look at the articles on KM and draw your own conclusion. And in particular note this article - see the comment from Ron Young at the bottom and the author's reply!