In case you didn't know, I'm a VideoLAN developer. I reverse engineered FairPlay and wrote VLC's FairPlay support. It's been available in VideoLAN CVS since January, but the first release to include FairPlay support is VLC 0.7.1 (released March 2.).
Just wanted to let you know that once you have generated the user key file(s), you can copy them to as many computers you want and play your M4P files there using VLC.
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.