I had never bothered with these little players or compressed digital audio since I presumed the sound quality was awful. WRONG! The little things sound great for serious music listening, presuming you click a couple of the right buttons in iTunes' preferences. I'll explain these in this article.
I converted all my mp3s to AAC months ago. I did it to conserve space. Awhile back, I started reading articles saying that mp3s are better than AACs. Imagine the stress!
This article kind of relieved all that stress. I hope he's right. But come to think of it, I never really did notice any difference...