I think the larger question is whether people could confuse this service for one by Pinterest - and I'd say the answer is Yes.<p>"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.<p>I say this from the perspective of someone who has received formal cease-and-desists from Facebook, Coke (<a href="http://bit.ly/17Tulqr" rel="nofollow">http://bit.ly/17Tulqr</a>) and a few others :)
"Ownership" of a word is not the issue here. The standard for trademark infringement is based on a "confusingly similar" basis. Unfortunately there is no hard and fast rule here: it's up to a judge to decide. That final points made in the article are exactly how one would go about mounting a defense; but again, you are at the mercy of the courts here and fighting this would cost.<p>(IMO the PinPigeon logo is indeed confusingly similar)
In my opinion, despite the protests, the logo has clear similarities to Pinterest's, and my first impression would be that it's trying to glom off of Pinterest's popularity.<p>I am aware they aren't identical, but that's not the relevant measure. The question is, could they confuse an average person, and in my opinion, yes. It is ultimately a question of what the judge would think, but I sure wouldn't care to stand in front of a judge and make that argument.
I hope Pinterest sends a C&D to Intel...<p><a href="http://software.intel.com/en-us/articles/pin-a-dynamic-binary-instrumentation-tool" rel="nofollow">http://software.intel.com/en-us/articles/pin-a-dynamic-binar...</a>
What confuses me is how Pinterest could get a trademark on the word "pin". It's a far too common word that logically could be used to represent virtual "pinning" of information.