Here are the links I found on my CDH3 tutorial setup. Second is recommendation guide https://mahout.apache.org/users/recommender/recommender-documentation.html
The org.apache.mahout.cf.taste.hadoop.item.RecommenderJob is a completely distributed itembased recommender. It expects a .csv file with preference for data as input. Here is an example of the csv file I inputted:
So at the end of the processing, I end up with a more data in file. Impressions: Mahout is for developers needing large scale processing of data with some limitations to algorithms. WEKA is mainly for data mining analysts and learners. The GUI and “autoAlgorithm” feature make it easier for beginners to process data. WEKA will have issues scaling to very large datasets because of memory limitations.