I just came across your post because I am having the same thing with my 5S, which I just posted a new thread on apple.com. The pixels seem more noticable than they did with my 4S or my wife's new 5S and like you said it seems to come and go. I was thinking it might just be me being picky, but than I came across your post here. Do you think it is worth exchanging the phone? Will the store have any problem replacing it?