Read the full article for some timely speculation from Cringely
Here is what I think is happening with the Apple TV hard drive. I think sometime this summer Apple will ship a firmware upgrade for the Apple TV and it will suddenly gain an important new capability. That's when the Apple TV becomes a node on the iTunes peer-to-peer video network.
If the Apple TV is plugged in it is turned on. Did you notice that? That means the hard drive will have at least the capability of running 24/7. Now envision a BitTorrent-like file distribution system that is controlled primarily by iTunes, rather than by you or me. A centrally controlled P2P system is VERY powerful because it allows for the pre-positioning of content.