Image: Wired
This is an interesting piece by Wired on Piotr Wozniak, a Polish scientist, experimenter and founder of SuperMemo. The spacing effect is a phenomenon discovered by Hermann Ebbinghaus circa 1885 which results in dramatically improved learning by correctly spacing practice sessions. Wozniak uses the spacing effect to power Supermemo, which reminds you of a piece of information that you are learning, just as you are about to forget it, which is the best time to revise it according to Ebbinghaus' and Wozniak's research.
Source: