Quick Start and Overview
Pentaho Data Mining, based on Weka project, is a comprehensive set of tools for machine learning and data mining. Its broad suite of classification, regression, association rules, and clustering algorithms can be used to help you understand the business better and also be exploited to improve future performance through predictive analytics.
Documentation
Pentaho Data Mining (Weka)
There is a book that has been written to accompany Weka - Data Mining: Practical Machine Learning Tools and Techniques (Second Edition). 
Plugins for Pentaho Data Integration (Kettle)
Developing with Weka
Awards and Publications
Under Development
Archived
Further Links and Information
