i have a 16gb black, with a little light leak on the left, nothing major and thats about it.
no cracks
no pixels
i think my black is a little negative compared to someones 8gb black iphone that i saw, but that could just be the 8gb are a bit diff than 16gb.
im just nervous if i exchange it that i will get somethin worse and since mine isn't that bad i should probably just keep it and enjoy it.
From my own personal experience, you certainly get anything worse. So if they agree to replace it, you can check it right in front of them and only leave if you're happy with what you've received.
I received two refurbs right at the genius bar with dust under the screen, and the genius didn't even give me the option to take the replacement phone. He just went into the back and replaced that one with a new one. When i left, i had a perfect, brand new phone.