Early adopters know the risks of grabbing the first batch of a first generation device. There are the inevitable kinks of the initial design that are just waiting to be ironed out in subsequent refreshes.
The iPhone 4, while it is the fourth generation of the iPhone, uses completely new hardware. And the early adopters who have been playing with their iPhone 4 are finding some flaws in their "Retina Displays" and metal band antenna.
Specifically, some users are seeing yellow spots and bands on the screen, as can be seen in the image below.
Time will tell.