I don't really see the difference between having your quilt hang at a show, where many, many people take pics of it, or posting it on a site and having someone pin it. I look at other people's quilts all of the time..never to copy them exactly, but for inspiration..maybe I like a color combo on one, or the quilting on another...
We have to remember to encourage and inspire each other!
Pinterest is just an on line bulletin board..no different than going to see a quilt, taking a pic, then coming home and putting the pic on your old cork bulletin board.