Podcasts have indeed revolutionized learning in the 21st century. For students unable to attend live sessions, or who, as you mentioned, would like to hear the session as often as possible, podcasts serve that need. How far we've come from my undergraduate days, when one needed to carry a micro recorder to a lecture in order to be able to hear the session over and over again! I think I failed to mention that when I have used podcasts in my own sessions, my students' feedback was tremendous. They, too, appreciated the portability of lectures, chat sessions--essentially, audio course content. Some students shared with me how they'd listen to the podcasts during their commute to and from work; others appreciated an audio presentation of the material. It was a great way to put into practice the concept of MI (multiple intelligences) in as many ways as possible.