1. AppleTV connects directly to the Net. Software and firmware upgrades will be sent right to the box, and not through your iTunes link. The movie and TV trailers are streamed straight from Apple too. I asked why they didn't offer a way for people to shop or browse directly from the device rather than through a PC...
...but the Apple folks didn't want to get into the specific reasons. I'm guessing that adding a keyboard would have defeated the point of this device. It really is an iPod for your TV.
2. AppleTV will pick up where your iPod left off. Let's say you start watching a movie on your iPod, then pause it 20 minutes in. Go home, plug the iPod into your host machine and then cue up the same film on the AppleTV and it will re-start right from where you paused.
3. Your iTunes season passes are automatically pushed over to your AppleTV's hard drive, and the episodes you've already watched will be removed automatically.
4. Photo libraries are copied to the hard drive and do not stream from iPhoto. Not only that, but AppleTV also does some crunching to optimize the pics for your widescreen display.
5. AppleTV synchronizes in the same order as the tabs on the device menu screen.
6. You can't delete the shows on your AppleTV hard drive through the iTunes interface. So it's not exactly like an iPod either.
More to come...