This will probably be hard to do in the short term but if MOOCs take off it would be good to actually verify if the reviewer actually has taken the course. I think that's one key issue with Yelp - there is no verification of reviewers so there are a lot of spam issues : http://thecaucus.blogs.nytimes.com/2012/09/09/obama-gets-a-l...
Maybe you can talk to the Udacity/edX/Coursera guys to get some kind of API access? Regardless, this is awesome - I've taken two courses on Udacity, and love it so far. However, there has been an explosion of courses offered so it would be nice to have tools like this to help me filter.