Course descriptions have been an elusive piece of data for many developers at the UW for some time now. Some developers resorted to screen scraping the UW time schedule, a set of html pages, to get access to the data however those days are behind us now. Course description is now available in the Student Web Service with our most recent V4 release.
Here is an example: https://ws.admin.washington.edu/student/v4/public/course/2009,summer,CSE,100
We are still looking at the possibility of delivering Instructor Submitted Course Descriptions.