I hate to say it, but it seems like a rehash of the recently emerging concept of paying for and selling "pins", "likes", and "tweets", only they are more professional and sugarcoating about it, even though it is technically a black hat concept. In the past, I've come across similar services that will pay you to tweet, if you have enough followers, "like" if you have enough friends on Facebook, and now "pin" for Pinterest. There will likely be no end to how many of these services take root in an attempt to make a profit off of what an advertiser pays for a user to one-up their product promotions and whatnot on a social network.
As with all services like this, there will be some that are scams and some that are legitimate. I would say that Pinbooster is pretty legitimate based on the effort put into the site, although the owners could put in a little more to make it look more professional. I see some buttons that don't seem entirely "in place" and I have to highlight some text to read it properly against the background, but that may just be my browser. Don't knock it until you try it, I suppose.