Learning is not about knowing facts, that's the least aspect of it. Learning is about making you able to think.
Anyway, I think automated grading could work for anything math-based, as well as for some computer programs. Consider that much of learning is done through homework and exercises that build upon previous exercises. I spent many hours learning by working through problems and checking my answers with an answer guide. (And being infuriated when I found mistakes in the answer guide!) Doing homework isn't a complete education, but it sure is a part of one. And yes, as long as the exercises are well designed, they make you able to think.
Needless to say, grading essays and whatnot is another ballgame altogether.
Basic programming? I am working on that: http://www.spoj.pl/AKADEMIA/
(note: Polish only)