FORTUNE — In a press release issued Thursday, Apple (AAPL) announced that content from its iTunes U site has been downloaded more than 1 billion times since the free educational service launched in May 2007.
There are now individual classes with more than 250,000 students enrolled in them, according to Eddy Cue, the senior VP in charge of the site, and not just fun stuff like the TED lecture on Understanding Happiness. All of the classes featured on Apple’s Most Popular Courses page have recorded at least 50,000 downloads and many require some heavy lifting, like Ohio State’s General Chemistry class (100,000 downloads the first year) and UC Irvine’s Environment Psychology class (170,000 students enrolled).
My favorite is still Michael Sandel’s Harvard University class on Justice, which starts off with a bang with an 54-minute lecture on The Moral Side of Murder and The Case for Cannibalism.
Below: iTunes U’s five-year growth curve.