[spiffytech]

Very neat! This is actually an implementation of "spaced repetition", a learning technique that's been employed for many decades. The Pimsleur foreign language courses, famous for their efficacy, use it.

For folks less interested in injecting this into their terminal, check out Anki. It implements spaced repetition as flash cards, and automatically computes how often to show a card based on how often you say you already know the material.