Not sure if Pinterest started this trend, but their signup process is genius. You need to get an "invite" to join, which always arrives within 48 hours. It ma

Not sure if Pinterest started this trend, but their signup process is genius. You need to get an "invite" to join, which always arrives within 48 hours. It makes you want to join because it's a "privelage" to be accepted. It's very subtle, but smart marketing.