Pinterest (pinterest.com) is a social network website all about sharing images which you "pin" to your personal "pinboards".
Pinning maps on pinterest
You can pin any image to pinterest, including maps! Some people have used pinterest to make some interesting collections of OpenStreetMap related map images.
Pinterest is kind of interesting when it comes to copyright. When you pin an image it takes a copy from a source website and stores the image on pinterest, and yet it encourages users to do this willy-nilly, for any image on the web, claiming "safe harbour". See wikipedia:Pinterest#Copyrighted content. If you are enthusiastic about complaining to people when they seem to be violating OpenStreetMap's copyright, you'll need to read up on how this nuance of copyright law is working (and you will probably conclude that there's no point complaining about people pinning map images)
Pinterest using OpenStreetMap
Pinterest used OpenStreetMap for map displays on their website, however the featured appears to have been removed (? everyone else not seeing it?). pinterest blog post announcing 'place pins'. The map rendering and hosting was by Mapbox. Mapbox blog post about it. There are/were maps on the iPhone app too: another mapbox blog about this.
Official 'OpenStreetMap' pinterest account
The official OpenStreetMap' pinterest account was created and is managed by the OSMF Communication Working Group. If you're interested in pinning more there, you'd be welcome to join CWG to make it happen!