My only bit of bashing is I don't like anything about the Mac...
On topic:
I would make the Mac accessable to some not so common things. As I usually work with audio codecs, bring not so common formats to the people that want things easy.
I would revamp iTunes and iPods so that they are compatible with not so common but free audio codecs. Starters would be FLAC and OGG Vorbis as many in the audio world push these codecs, I myself included. After that WavPack (WV), hybrid WV, and CUE-sheet & *-images.
Easy way to get most of that support on the iPod is have it with
Rockbox (Released under the GNU). I would make the iPod dual boot Rockbox and iPod software.