I found that on the larger playlists, doubles of the same song would stop the copy. Make sure you use "show duplicates" on your playlist, clean it up, and then everything should be fine.

how often do you need to pull a cork out of an -empty- bottle?

For mac users, you can also use

So you'd have to do this on every Windows machine you'd want to plug the Zune into to get the files -off- too, right?

Or, alternately, take a picture every six minutes for 24 hours.