The rate of Pinterest visitors making it to my website is next to nothing, so there is no marketing windfall to be had from Pinterest. I think people view the pin boards, click to see the full size image of what they like, and don't bother with the original website.
That is my observation.
I'm not keen on watermarking the images, it's defacing my own website - cutting off my nose to spite my face.
I'm going to block pinterest as a referrer on htaccess. I'll post my results.