Zune Wireless Song Sharing May Not Be All It’s Cracked Up To Be

Wireless song sharing is a big part of what Microsoft is using to differentiate it’s new player from the iPod and others. But this line in last week’s Zune announcement has bloggers buzzing:

"…users can listen to the songs three times over three days before deciding whether to purchase it themselves."

What kind of DRM is Microsoft attaching to a shared song to make this little trick happen?  And what happens to a song when it’s no longer playable?  Does it just take up space on the hard drive?