You dont put a single dime down, so its not a pyramid scheme
IMO, a pyramid scheme doesn't necessarily involves money. On this case, they are betting on users doing the advertising for them, wasting their personal time, and in return they get some type of reward as motivation. I've enrolled on websites like this and it's always the same crap: "Hey, invite all your friends, the more who signup, the more you earn" and in the end you'll only earn some miserable amount of money, or some lousy t-shirt, despite all the time you spent being a nag to your friends/colleagues/known persons. Either way, the world's population in general is not prepared for social networks, facebook has proven that. I mean, posting useless shit and wasting resources for cat pics is not the best use for a social network, am I right?
Edit: BTW, I love it how all your links have some kind of code, what is that about? (hint hint)