Microsoft's Zune won't play many DRMed Windows Media files.
This is a stark example of DRM under the DMCA giving customers a raw deal. Buying DRMed media means you're locked into the limited array of devices that vendors say you can use. You have to rebuy your preexisting DRMed media collection if you want to use it on the Zune. And you'll have to do that over and over again whenever a new, incompatible device with innovative features blows existing players out of the water.