I don't know. If we are talking about artistic work, it'd probably be fine with the proper attribution, but if it's a recipe, that's the entire content with no additional point of visiting the original page.
Then again, this is in no way different than Tumblr, which is the most egregious copyright offender, even within its own ranks because of the reblog feature. Recently, the actress Dianna Agron - known from TV show Glee - launched her own website http://youmeandcharlie.com, which does - and encourages - the same thing. And it's building a profitable business on this model, meaning that the people behind the site earn money based on this approach; it's one thing to have a random Tumblr account with no financial incentive, but this is different.
The biggest problem is that we suck at teaching people and our children the importance of proper attribution, and why it is important that we do our best to tie the author together with the work. I don't know if this requires a taboo or campaign, but with services like imgur and Tumblr, it's only going to become a bigger problem - and that's not to discuss how the majority of reporters don't get the point of sourcing either.
I think an ad-hoc approach to dealing with DMCAs - and possible blocking specific content hashes - is the only way to do it for Pinterest. Anything else hurts Pinterest as much as the content owners and shops.