Google Knol, Mountain View's answer to Wikipedia, launched last week and, while it can't yet match the volume of articles on Wikipedia, its focus on accountability and ownership makes it a better choice for students and teachers.
Consider the article on asthma by John Fahy. According to the knol (a knol, according to Google, by the way, is a unit of knowledge), John Fahy is a professor of medicine at the University of California, San Francisco. Google notes that this has been verified and a quick search for Fahy turns up his biographical site at UCSF. Try getting that information at Wikipedia about one of the authors.
I've always been a fan of Wikipedia. The amount of information available on the site is extraordinary, free, and usually a fairly accurate starting point for research or quick answers to questions. However, it has no accountability other than a community that can edit and comment on an article. Knol, on the other hand, removes contributors anonymity and gives students the ability to verify sources of information.
Will it be able to grow as quickly as Wikipedia? Probably not; plenty of people with subject matter knowledge simply aren't willing to put their names and faces on the web. Is it an inherently more reliable tool that can improve students' research capabilities? I think it is. It will be interesting to see how this competition shakes out over the next school year.