usefulness...
j5045096, AppleTV is incredibly useful, if you want it to be. Besides the obvious "front row" like experience you get with your MacBook Pro, you have the iTunes Store, which is great for the HD (720p), but nicer still is the way the file is downloaded, allows you to watch within minutes of buying or renting, so unlike your MacBook Pro, you can watch almost instantly.
I have two AppleTV's my own and one in the family room. Both synced to my iTunes Server based on a PowerMac G4, and then linked streaming to all the other macs in the house, (PowerBook G4, MacBook, Macbook Pro, iMac). So it's nice to share the households content.
Depending on your individual needs, you could either love it or be indifferent, but I think all AppleTV owners love this little "hobby" device.