I left them a comment doing just that, but there's been no reaction thus far - presumably, some assistant is maintaining the board, and who knows how many comments they might get in a day. Pinterest doesn't provide a way to contact other users privately that I can find.
That said, a couple of hours ago I wrote to their press email address for people letting them know about stories they're going to write about Pinterest, and told them I was planning a press release about their poor handling of spam, based on this experience. I've gotten a response from a live human apologizing and saying a team member will look into it as soon as possible. (Whenever that is, right? LOL.)