User-testing does not result in brilliant design. That requires brilliant designers. User testing guarantees that whatever level of design a company has been able to achieve will actually work.

Bruce Tognazzini – comparing the iphone and the kindle.  And he goes on to say that:

There are no trade-offs here. Human/machine interaction is a subset of the user experience. Anything done to improve the mechanics of the interface will, by its very nature, improve the overall experience. Anything done to improve the user experience will amplify the good qualities of the human/machine interaction.

You must, however, research and design each of them separately—and to test each of them separately. They each require a specific frame of mind, and concentrating on just one will lead to the kind of uneven design that both the Kindle and the iPhone/iPod Touch have been offering.