I was just reading a Technorati article entitled "Pinterest Users Need to Read the Fine Print". It discusses the issue of Pinterest users agreeing to granting Pinterest the rights to use everything they pin on their board for free, forever. Not such a huge deal, except, if it's not your content, you're not legally authorised to grant Pinterest that right.
So if you pin a poem, photo or recipe without the poet's, photographer's or cook's written consent to redistribute their work (which is what you're doing), you're breaking the law.
Copyright laws meet social, on-line sharing. Services that facilitate sharing cover themselves, and provide remedies for copyright owners, leaving those sharing left vulnerable to legal ramifications.
Similar issues have existed with the sharing of movies and music, but now it's compounded by the legitimisation of the sharing of copyrighted materials. The only way facilitators can provide a medium for sharing is to have the right to share, but we, the users, cannot grant them that right.
While this is inevitably going to lead to increased litigation, at least in the short term, I predict a huge shift in the way we regard copyright and sharing. Already the movie industry is encouraged to relinquish their dependency on litigation and traditional sales media, and accept that sharing is the new black.
Could it be that sharing is becoming the next currency?