My initial impression of Bump is that it was a silly idea. Like what if you damage your phone. However, the secret and success of Bump is that it makes a boring transaction a little more fun. Bring back a little human interaction. Make the people using it look cool or uncool (depending on the audience) - but regardless make people pay a little more attention to the people bumping. Everytime, I see a public Bump, I get amused.