I'm a big fan of spaced repetition. From a mathematical standpoint it's also a very interesting question: You have your forgetting curve and which gives you the probability that you still remember the association. I think there is still some rooms for improvements around there. For instance, I'm not sure if the big plays in the area adjust the forgetting curve for each individual user after they have enough data points.
Shameless plug:
I actually just developed a new spaced repetition platform the last few years. I'm not official launched but it's online and works. If anybody is interested in taking part of the beta testing, email is in my profile.
Shameless plug: I actually just developed a new spaced repetition platform the last few years. I'm not official launched but it's online and works. If anybody is interested in taking part of the beta testing, email is in my profile.