I've signed up for it! I put in my profile and everything. Then I started reading the articles, and I realized these were long magazine articles, written for professional credit. I hate that! It reminds me of the old company, where each boss only wrote things in newsletters, for their boss to read. Thus, everything becomes rather boring.
One thing that exited me with Wikipedia, before it was taken over by militant editors, was the fact you could break things down to single page articles, and build things up with links. That way you could write for Grade 10, and yet if somebody followed all the links, it would be almost university grade. Knol has no links, since everything is privately held, and it is all written directly for university. Unlike the wiki, this makes it very reputable, but not very innovative or modern.