There is certainly solid legal ground for arguing that Google giving preferential search results to itself is an anticompetitive practice. It would be different if Google didn't control the vast majority of the search market, but it does.

Let's say there is a phone book company that pretty much controls the entire market. Google's actions are akin to the phonebook company only listing businesses that it owns in the main pages, while listing everything else in an appendix. Anticompetitive practice, to be sure. The phonebook company might argue, "Well since we are so tightly integrated with out own businesses, it is much easier to index them. Our competitors ending up in the back is simply an unintended side effect". Possibly true, but it's not going to fly in court.

To be honest, I don't care if Google is giving preferential treatment to Knol. But please, establish some plausible deniability. The speed in which Knol is being indexed is far too obvious. I think it would be a damn shame if Google were to lose its hold on the search market because of a lawsuit.