I have to admit. On this one, I'm far behind the technology curve. For some time, I've been constantly chewing on myself to get an IPod (I'm not even sure about the grammar. Do you capitalize both the I and the P? Just the I? Or, maybe you leave the I as uncapitalized "i". It's a brand name, so it's hard to tell sometimes.)
The strongest use of this would be for subjects and media geared around sound. I.E. Music, Talk Radio and News and Old-Style Radio Programs. Personally, I've always been a fan of the comedies of the Twenties, Thirties and Forties, such as W.C. Fields and Abbott & Costello.
Education would be useful as well, particularily the literature and second language podcasts. I listened for a while to some of the Shakespeare podcasts on the Education Podcast Network. Very Nice. Hearing the words spoken, rather than slogging through the reading(and the numerous footnotes) would be a big help to students.
Other subjects, like math or chemistry are more visual, but the podcasts can be a good suppliment, particularily with the vocabulary or definitions. Stuff like that.
Used in conjunction with Youtube, just about every subjust used for distance education should be covered.