I refuse to use any Apple product,
but I do have a 30-GB Zune that contains maybe up to 6 hours of digital music (almost all of which were burned from CDs I used to have). Audio books sound fun ... anything you listen to can make your workout seem to go faster.
Going back to Wii Fit, I have a couple of co-workers who use the console for their yoga and indoor exercise routine. They seem to like the interactive features.