A Year of Spaced Repetition Software in the Classroom
Not directly related to duolingo but I think a very good writeup of one teacher's experience of using SRS in a related context.
Good article. Are you familiar with Quizlet? It is also a free card sight. What advantages might Anki have over Quizlet, as I have briefly given Anki a try, but don't see any immediately. Granted, I haven't spent much time on it.