> "The viral loop probably lies in encouraging people to sign their existing friends up so that we can better classify the kind of people a user gets along with."

So something like: 'Hey friends, some of you should spend your time to take this online questionnaire, so that I can benefit by having this site find me some other people to hang out with besides you lot. Also, if you think it is a jerk move for me to ask you to help me replace you in my life, then the site might be able to help you find someone similar to me who can fill my slot in the social circle.'