An army, worthy of Mordor.

Restriction: you can't say a Facebook competitor/clone.

Don't know about building, but having a list of someone's friends must provide some excellent ammunition for fraud. Eg. you could do the Spanish Prisoner scam using peoples' friends' names. Most attempts would fail of course, but you'd be doing it in bulk over the web, from a safe distance.

I'd be really tempted to judge you by the company you keep, and put Fair Isaac out of business.

Some sort of uber pyramid scheme ... just as an experiment to see how big it could get.

You know that saying "everyone knows everybody over 6 other people", maybe something about that. Or: who of your friend's friend's friend's has the same hobby / whatever.