Goodereader.com posted today that iTunesU has passed the 1 billion textbooks download since opening in. iTunes was launched in 2005 as a partnership with Stanford. The partnership expanded to more schools in 2007 and then this last 2005 year a dedicated app was released. Now there are more than 1200 colleges and universities and more than 1200 K-12 schools using iTunes U.
That seems to be a pretty big deal. More info at goodereader.com