I'm not super familiar with Pinterest personally, but from what I've read, they drive significant amounts of traffic around the web, particularly to e-commerce. My understanding is that it is like Reddit, but with thumbnails. That seems (to me anyway) on the right side of the line.

Sites like FunnyJunk drive no traffic anywhere. They're built to suck in other people's content and keep all the traffic on the FunnyJunk servers.