To my way of thinking, no permission is not needed, but most of us would like to know that we've been pinned. ("hey, I liked your quilt so I pinned it. Thanks for sharing"). Mostly as an ego boost
Also, even though I keep my pins in locked accounts on Pinterest, I always try to make sure that I keep the link to where I got the pin - especially if I need more information about the quilt.
The fact is, once we've uploaded a picture of our quilt to QB it is totally accessible to EVERYONE (not just QB members).