The 'Source' command on Pinterest

I discovered this today.  I'm not sure how widely known it is, but if you use a 'source' command in the URL - see below - you can see the pictures on Pinterest pinned from a specific site.

E.g.

http://pinterest.com/source/apple.com/

or

http://pinterest.com/source/nike.com/

or

http://pinterest.com/source/lisastickleylondon.com/

or

http://pinterest.com/source/magnumphotos.com/

or

http://pinterest.com/source/flickr.com/

Or even 

http://pinterest.com/source/shutterstock.com/

& finally 

http://pinterest.com/source/emarketer.com/

You can see the most popular content from a site.  It makes it a brilliant source for all kinds of research!