To complete the work started in
MAHOUT-389, I've created a distributed version of any item similarity function that is currently already available in a non-distributed manner. An additional M/R job was necessary to compute the number of all users which is needed by some similarity functions (like LogLikelihoodSimilarity for example).
There is still some optimization potential in the code as not every similarity function needs all information that is currently extracted (like the number of users e.g.), but the optimization would have made the code much less readable so I did not do any work on that.
I hope you consider this a useful addition.