Wealthy business people who have to constantly make a good impression to keep up profitable relations sometimes employ personal assistants to study their acquaintances. The PA then stands behind the wealthy person at social events and whispers a few choice words to him or her about someone who is approaching to converse. The words have to be succinct but informative, such as "Paul Smith. One child, Jill. Recently travelled, Mauritius". Now, our business person can pretend that whoever has approached is a dear friend and talk all about his children and travels at some length without having the faintest clue of who the person actually is. This makes other people feel important and liked, and this can help our hypothetical millionaire become even richer.

Why is this relevant to web applications? Well, we want to do exactly the same thing. Users of our site who feel important and remembered are more likely to come back, so we need...