The main reason I haven't ditched my iPod is the interface... unfortunately, so many manufacturers got on board with iPod that it's pretty much the only device that gives a seemless interface with things like car stereos (such as mine, where the iPod goes in the center console and I get full control + song information on my dash).
I don't think we'll be seeing that with "other" devices for a looong time, and it's tough to beat.