Well, if you haven't read Walt Mossberg's review of AppleTV yet, this is a good place to start. Of course many people will argue that the AppleTV is a niche product, or has limited content, or doesn't have DVR functionality or this or that. Personally, I've already come up with a great use for the AppleTV that fits my needs and possibly the needs of millions of people.
Tivo. But wait a second, AppleTV isn't a DVR. That's not my point. My focus is the subset of people out there who have a Mac, already have Tivo service, and have two or more TVs, but have only one Tivo. Now Tivo is great, but is made better by TivoDecode Manager(TDM) for the Mac. For most TV owners, the TV content is stuck on your Tivo and one TV unless of course you don't mind watching your TV shows on your computer. But that is exactly what AppleTV is here to solve. Moving content away from your computer and to your TV.
With TDM I can batch queue all the new shows on my Tivo to have them converted to an iTunes compatible TV show or movie while I am asleep or at work, ready to be watched in a different room at my leisure. Now I don't have to fight over what's on the Tivo and be limited to watching it on the one TV that it is hooked up to. Of course I could always take the plunge and purchase another Tivo and record even more shows, but in reality, there aren't enough TV shows to keep a Dual-Tuner Tivo busy. Plus, by the time I purchase another Tivo and then the monthly service, I've already sunk another $350 into Tivo.
Of course there are plenty of other ways to use the new AppleTV, and everyone will find a way to make it work for them, but as always, this is just my $0.02.