I've found dresses that are tight in the bust WILL stretch in that area. I have two dresses that were super tight in the bust and now when I lay them flat there is a little puckering there. They still look great on, though. Also, I have a v-neck dress and the seam has sort of started unraveling -- like vhdos said -- but not really. I was worried at first when I saw the threads starting to stretch, but I've worn it about 20 times since and nothing has happened...yet.
My dress came today -- sorry for the crappy picture...what do you guys think? I think it'll look better when I have a tan...but really...should I keep it?