I signed up for this forum just to reply to this thread and share my experience. Got a new 4S, which is awesome coming from a 3GS, and there was a very conspicuous dead pixel on the screen. Probably a cluster of them for it to be so obvious, but just in one spot.
I bought it at Radio Shack (which agreed to give me a new one, but not for a while since they were completely sold out) but took it to the Apple Store for evaluation. The "genius" I saw said that it was within acceptable parameters and that I'd just have to live with it.
I made an appointment at the same store the very next day and saw a different genius, who looked at the dead pixel, nodded, and promptly got me a replacement. The new phone actually has a dead pixel too, but it seems to be just one and, frankly, I sometimes can't find it even when I'm looking for it. It's fine by me and I've been enjoying the 4S tremendously since.
I guess the moral of my story jibes with what I've read on other forums: a lot depends on the whims of a particular genius, so if you don't get the help you want the first time, come back (or go to a different store) to see another.
Best of luck!
