IANAL, but I think trademark violations don't hinge on just one element (i.e. name, or in this case, prefix). It's the combination of the name, logo, and the us

IANAL, but I think trademark violations don't hinge on just one element (i.e. name, or in this case, prefix). It's the combination of the name, logo, and the use of a pinterest.com URL as the central piece of this service, which might confuse users, thinking this service is affiliated with Pinterest. I think their letter explains this pretty well, and I couldn't spot the "threat" in it? There was just a vague hint of "consequences". BTW, http://pinteresf.org http://pinteresf.org now redirects to pinterest.com. I wonder if they got a similar letter, and as a result handed over their domain?