I'm late to linking to this, but this piece by John Gruber is superb:
You need to recognize a Porsche 911 as a 911. An iPhone needs to look like an iPhone. The design needs to evolve, not transform. The thing to keep in mind is that the iPhone itself, what it looks like in your hand, is the embodiment of the iPhone brand. There is nothing printed on the front face of an iPhone because there doesn’t need to be. The Apple logo is the company’s logo. The iPhone’s logo is the iPhone itself.
This is John at his best.