I am in favor of the "0" button as well. I like the ability to see a particularly difficult card multiple times in one pass rather than the following day or two. Even seeing a difficult card every day makes it hard to lock it down, seeing it over and over during one study session is one feature of anki I really like.
Explaining priorities / difference between web and mobile/beta -- this should help with the "0" card discussion.
The web works on a calendar based system. Based on all the input on a card -- the rating, how many times you've seen it, etc., every question is assigned a datestamp -- a day you should do that question. So when you come any given day, you have a set of questions to answer. If you miss Monday, on Tuesday you have to do Monday and Tuesdays questions.
The beta / mobile work on a priority based system, that updates constantly. Every card is assigned a priority value that constantly changes, based on your rating, how many seconds you looked at the card, and how long since you've seen that question.
So in the priority system, a card you've seen once and rated a 1 will be placed back in your stack and will have a high priority. Most people will see that question again very soon, but it depends -- how many other cards do you have rated a 1, or how long has it been since you've seen them? Questions you rated a 5 months ago will have a steadily rising priority as time goes by. And if you have a lot of questions you rated a 1 a week ago, they may come up before the card you just rated a 1.
So, if you rate a card a "0" or a "1" and want to see it again very soon -- when should you see that question? What if you are on question 78 of your daily 80 question goal? I've never used Anki so I don't know how they drop questions in (see it again in 10 minutes is what I've been told), but the way Firecracker's system works makes that a difficult inclusion. Some users could have 200 questions they just rated a 1 that have a higher priority than the card they just rated 1.
This change was not undertaken lightly -- we collected thousands of score reports this summer from users, and with their permission looked into how they actually used the system. We looked at the most successful users, how many questions they did a day, did they keep up with their calendar? We looked -- did the calendar accurately reflect the likelihood of a user getting a question right / rating it a 3-5 the next time? I.E. -- if a user did not answer a question on the day it was assigned, did that materially affect the likelihood of them rating it an improvement from their previous assessment -- raising the count by at least 1.
Our stats team believes the priority based system makes more sense than the calendar based system. So there is no "daily count" anymore within the system. Instead, all cards are prioritized, can you can just keep going.
Some things that are coming soon:
---You'll be able to change your daily goal from 80 to whatever you want, 1-999. Look for this in beta this week, then in Android, then iOS in a couple weeks.
---You'll be able to create custom playlists. So if you want a playlist of just renal, or a random assortment of topics for an upcoming class exam you'll be able to create separate stuff. "Do Today's Questions" will prioritize questions from all playlists. Shooting for January on this.
---You'll be able to set dates on playlists, such as the date of an exam, or the date of your USMLE. That will help to generate a "suggested daily goal" based on the number of questions and a multiple of how many times you should see the cards. Could come with the above feature in January, but shooting for next 60 days.
