There's precedent that would make it in Pinterest's best interest. IIRC Google's "Panda" algo update basically wiped out search referrals to certain content farms overnight, can't recall specific examples but there were some at the time. They were labelled as low quality and subsequently faded into obscurity.
//added
EHow is an example of a site that was flagged
//added EHow is an example of a site that was flagged