I had a conversation with a colleague this morning about student iPod use, and it came up that we (adults) tend to use iPods and other mp3 players differently than students do.
For students, iPods in class tend to be distractions and an escape. This is likely the source of teachers' objection to these devices, that they detract from student learning.
For teachers themselves, or at least for me, an mp3 player is more of a professional development device. I'm usually listening to podcasts, lectures, and audiobooks, and many of these are education, or at least technology, related.
And I don't listen to my iPod in class.