I know this has been discussed before by people who understand it better than I do, but I feel it needs to be said again. I know that spaced-repetition does not work well if reviews are neglected, but what really does not work well is if the system wants you to review so many cards that you stop using flashcards altogether. The problem is particularly acute if you miss a day - often because you are busy, which not a great time to be loaded with extra flashcard work. The next day, you have double the number of flashcards due, and there is nothing to do but slog through it if you want to get back to normal amounts. From my perspective as a user, this is problematic as I don't have the time, and de-motivating. I don't want to be a slave to the dictates of my spaced repetition. If I'm busy for a day, I don't want my flashcard system to punish me for it. What I would like to see would be a simple way for the user to determine or limit the length of a flashcard session, and have the spaced-repetition adapt to my needs and not the other way around.