Curious about this, I conducted a test of my own. I pulled down the top 50 songs downloaded from Zune Marketplace, using my Zune Pass subscription. I then created a playlist of those 50 songs, and attempted to wirelessly send the whole playlist to my wife's Zune.Link (Via Deep Links)
When the transfer completed, a message appeared on my player: "Can't send some songs because of rights restrictions. 29 of 50 songs sent to Carrie's Zune".
I write books. My latest is a YA science fiction novel called Homeland (it's the sequel to Little Brother). More books: Rapture of the Nerds (a novel, with Charlie Stross); With a Little Help (short stories); and The Great Big Beautiful Tomorrow (novella and nonfic). I speak all over the place and I tweet and tumble, too.