It's "music to my ears" when students post a journal or tell me personally how much they've gotten out of the course or a particular topic.  This motivates me to continue to facilitate their learning using the many media methods and my skills.  However, one of the things that jazzes me the most is when a student tells me that he/she has learned to be a better thinker in general (i.e. more logical, more tolerant, with fewer self-contradictions, etc.).