My teaching philosophy has changed radically over the nearly 20 years of I've been involved in undergraduate teaching.  When I started, I lectured the students, because that was the way I had been taught during my own training.  But I was always frustrated by the fact that many students didn't seem to understand the underlying concepts.  Gradually, I realized that for many students, if not all, doing was more powerful than listening.  So now I'm working to decrease the amount of time I lecture and instead increase the amount of time students get to practice, work on problems, struggle with readings, etc.  That's why I wanted to get involved in CourseSource, because CourseSource promotes that same philosophy.