Microsoft is trying to set its Zune media player apart from the iPod by showcasing its remarkably limited sharing feature. Many reviews have harped on how shared songs can only be played three times over three days. But the restrictions are actually even worse -- if you read the fine print, you'll find that "The Zune to Zune sharing feature may not be available for all audio files on your device."

In fact, Engadget reports that certain songs bought at Microsoft's own store cannot take advantage of Zune's sharing. All the songs come wrapped in DRM, and apparently Microsoft doesn't tell customers at the time of purchase whether songs can be shared or not.

The Zunerama blog tested the sharing feature on the top 50 songs sold at the Zune Marketplace and was met with this message: "Can't send some songs because of rights restrictions. 29 of 50 songs sent to Carrie's Zune."

As usual, when you buy DRMed media, you may be getting much less than the online music service has promised.