I just returned from a meeting/training that explained a little more about ITunes U and how it can be used.
Basically, some of the major universities, including MIT, Stanford, Berkeley, and others have put some or all of their course content online. In fact, some of the courses at Duke now require the purchase of an ipod, rather than a text book. These and others have used ITunes U as a one way to disseminate the information to everyone around the globe. This is an amazing resource. You can get to the ITunes U library and listen to many educational lectures or see presentations, video, slideshow w/audio, etc.
These resources don't cost anything, only to have ITunes downloaded on your computer.
The possiblilities of using these podcasts in the classroom are endless!
Check it out at http://www.apple.com/education/itunesu/
Official Announcement: http://www.apple.com/pr/library/2007/05/30itunesu.html