The delicious.com site and pydelicious are used in a large number of machine learning and data analysis tutorials. The examples are in the arena of "based on your links, find other links that would be of interest" or "given these tags, how would they best be clustered". I can build text files offline and upload them to work with, but I'd still like to request this site be opened up if it meets your other criteria for whitelisted sites.
Tutorials include - http://shop.oreilly.com/product/0636920017493.do - http://shop.oreilly.com/product/0636920025610.do - http://www.amazon.com/Programming-Collective-Intelligence-Building-Applications/dp/0596529325
Regards, Jeff Plummer firstname.lastname@example.org