This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
I think you need a good working knowledge of Java to use Mahout effectively, partly because you will probably want or need to look at the source code frequently. I would not describe it as "for beginners", but at the same time I don't think you need particularly advanced knowledge of Java to use it.