UNAVCO sponsored a short course on InSAR for beginners, Monday June 16 - Wednesday June 18, 2008, and ROI_pac usage was covered. See UNAVCO Short Courses for details and course material. The class was fully subscribed, so we will probably run it again.
One of the sessions was on ROI_pac "Internals". That presentation is uploaded here in PDF format. It explains the steps in a typical ROI_pac processing sequence, with examples of the output at each stage. Most examples are from the test data provided with ROI_pac.