Code works with BookCrossing data set, which is not included in this distribution but is downloadable from
http://www.informatik.uni-freiburg.de/~cziegler/BX/

Data set originated from:

Improving Recommendation Lists Through Topic Diversification,
 Cai-Nicolas Ziegler, Sean M. McNee, Joseph A. Konstan, Georg Lausen;
 Proceedings of the 14th International World Wide Web Conference (WWW '05), May 10-14, 2005, Chiba, Japan.
 To appear.