I heard about the site from a classmate, so I logged in and spent a few minutes adding my profile/resume info. Didn't really expect much, but within a couple weeks I was contacted by recruiters looking to fill internship positions. Got a couple interviews out of it. Pretty good considering how little time I spent on the site.
They will spam your entire mail account without allowing the user to choose who to invite. Therefore, the disclaimer that a "friend" of yours is inviting you to join their services is invalid unless you've kept your contacts in your mail account up-to-date. For example, they will spam Amazon as well as people you no longer deal with as long as they are in your account.