I'm a heavy user of anki, especially in my japanese learning, and I agree that it is one of the most efficient tool to help one remember things. Optimized repetition has its limits though, and I often find myself overwhelmed by too much cards. For language learning, I'm not sure that spending time rehearsing vocabulary anki is more efficient than reading new material (or, probably the best, expressing oneself in that language in a new setting), but it would be extremely interesting to test that.