Why has no one mentioned SuperMemo? The software has been around since the 80's. I use it every single day (because you have to) for about 30 minutes to remember Latin vocabularly. It's based on spaced-repetition. If you feel a particular piece of knowledge is worth remembering permanently, I would recommend using it. http://www.supermemo.com/
There's actually a Wired article about the author of the software http://www.wired.com/medtech/health/magazine/16-05/ff_woznia... Completely eccentric and totally devoted to using the thing. I mean he doesn't even decide when he responds to his own mail, Supermemo will "schedule" it for him. I believe the latest version supports something called "incremental reading" which Wozniak claims is better than the usual order we read things. You read till you get bored/tired and them move on and it'll keep track of where you were, etc.
There's actually an open source app which functions similarly to super-memo, but uses an older spaced repetition algorithm and doesn't quite have the same feature set. Its called Anki (http://www.ankisrs.net), and its been a godsend for both myself and many friends who learn Japanese.
The thing I found interesting in this article is that switching contexts actually increases the amount you can learn. From what I understand, this would mean studying grammar, character reading/production and vocabulary at the same time would be beneficial. I never quite understood why this was the case before, even though people have told me it is so.
I also heavily use Anki for learning (Japanese). Although you can learn all sorts of things very efficiently with it once you get into the habit of using it.
The program is great, it comes with >free< syncing/online backup, provides an iOS/Mac/Linux/Win/Android/Maemo client and a slick browser interface.
I really like that there are so many clients. Would really like some kind of cloud-sync + mobile client for SuperMemo. It also only works in Windows which means I have to run it under VirtualBox.
My only concern with Anki is whether it still uses some variant of the SM-2 algorithm and whether or not the people implementing the software are doing more than just polishing interfaces, etc. and actively work on improving the learning algorithm. Looking at the history, SuperMemo on SM-11 http://www.supermemo.com/english/algsm11.htm and Wozniak claims that there is a substantial evidence that this algorithm increases the speed of your learning.
Yes, Anki used to use a slightly modified version of SM-5 but the Lead-developer decided to revert down to a modified and improved version of SM-2. Basically he reasons (you can find his explanation on the Anki FAQ) that while versions newer than SM-2 are supposed to (slightly) increase efficiency, it only happens if you study every day and at roughly the same time of day. The reason is, that starting with SM-3 a failure on a certain card changes the difficulty of (determined by the algo) similar cards.
A further explanation by the lead developer can be found here: http://markmail.org/message/u2zfnrg7x53bzp24#query:+page:1+m... I am convinced that it (at least for me) offers much better studying conditions. (Actually, the mere fact that I can revise on a crowded 30min commute on my ipod would make up for any efficiency increase).
There's actually a Wired article about the author of the software http://www.wired.com/medtech/health/magazine/16-05/ff_woznia... Completely eccentric and totally devoted to using the thing. I mean he doesn't even decide when he responds to his own mail, Supermemo will "schedule" it for him. I believe the latest version supports something called "incremental reading" which Wozniak claims is better than the usual order we read things. You read till you get bored/tired and them move on and it'll keep track of where you were, etc.