I don't know if this is a stupid question, but I always wonder how do guys like Pinterest make money?
They have a very lovely website, it has a great idea and they have too much traffic. I can't see any banners on their website or a paid subscription. It's totally free I guess.
This question isn't only about Pinterest, this is what I have in mind now, but you know there's hundreds of other free successful websites. I am not sure if Twitter is too, because I don't quite use it, but from a generic look at the site it looks totally free and banner-free too.