The poorly named "SearchWiki" feature from Google is "a way for you to customize search by re-ranking, deleting, adding, and commenting on search results." Changes appear whenever you're logged into Google... and others can see the public comments that you leave.
If you haven't seen it at the Google for Educators site already, this project is getting more attention now: "With technology producing such dramatic changes in American politics, we want to make sure it's easy for teachers to bring some of the best Internet tools into the classroom to help students get engaged."
Google's explanation of their product set to compete with Wikipedia. I think wikipedia will still have an important place... and IMHO may still eclipse any attempts such as Googles, though I expect the knols will have a value as well.
As many pointed out today, Google bought Jaiku, a service similar to twitter. I wish I had created a test account earlier. They are now closed to new registration until the overhaul is done. Stay tuned...