I think the larger question is whether people could confuse this service for one by Pinterest - and I'd say the answer is Yes.

"pin" in itself isn't an issue but the logo and typography are visually similar and could lead to confusion. You also directly use Pinterest as part of this service.

I say this from the perspective of someone who has received formal cease-and-desists from Facebook, Coke (http://bit.ly/17Tulqr) and a few others :)