I just added myself to the following Frappr groups:

What is Frappr? The about page states the following:

Frappr was created by the zany guys at Rising Concepts, who wanted to see where all their high school and college friends went after they graduated.

Frappr (Friend Mapper) lets you see the zip code where your friends live or work, letting you find out who works in the office building next door and who lives in the apartment complex across the street.