Consumer Reports has been writing about Alexa for a while; the new issue (Sept) has new stories. Even if you are not a subscriber, you can read most of them.
Go to
http://www.consumerreports.org/cro/index.htm and using the site's Search box, just search for "alexa" and all articles will appear. You can refine the search further (e.g. by date range, etc). You likely will find something interesting to read; over 40 articles appear.