One of the more vocal and involved companies using Cascading has been RapLeaf. Vocal due to the feedback and questions they present on the #cascading IRC channel. Involved due to the level of detail of their feedback, and the serious number of boundaries they are pushing with Cascading as a compute model.
They have hard problems to solve to support their business proposition, and we are glad Cascading has made it easier for them to achieve their goals.
In that context, they just posted a short tutorial and overview of Cascading on their engineering blog, Goodbye MapReduce, Hello Cascading. Enjoy. (Thanks guys!)