This iPod design article is an interesting look at the hardware challenges Apple faced. From a user interface perspective there's only this: ' "First and foremost, the product was elegantly designed in classic Apple fashion," says David Carey, president of Portelligent. "They did product design from the outside in." Carey says the company had a vision of what the player should be and what it should look like. The subsequent design parameters were dictated by its appearance and form factor.'
Link courtesy of David Wertheimer.