Got my Premium one (the one with the wireless controller, DVD remote, live headset, and hard drive) for Christmas...and so far I love it...lemme count the ways:
1) The remote AND the wireless controllers can power the system on/off. No more getting my lazy butt out the chair to start gaming. (Unless I need to switch the disc, but that don't happen too often.) You can stop a game and go back to the dashboard without rebooting now also, right from the controller.
2) Being able to recharge my wireless controller's batteries WHILE STILL PLAYING, and even with the headset on.
3) The HD resolutions are absolutely amazing. If you're not playing games at 720p or better, you're not seeing what I'm seeing.
4) The online integration kicks major booty. The Xbox360 will set up and maintain a connection to Xbox Live any time it is booted up. (This can be disabled, also). Even if you're playing a game offline, you'll still receive messages, and notifications when your friends sign on. You can pause your game, enter a live voice chat, and continue that chat while you're stil playing. And if you ARE online (say in a multi-player game of Perfect Dark Zero), you can choose whether you're talking to your team or one of up to four separate private voice chat rooms.
Basically, its a voice-enabled MSN messenger built into the Xbox Live system, and always on. It also keeps track of people you have SEEN online, in case you want to add them to your friends list. AND, your achievements in any offline or online games are tracked PER GAME, giving you a total numerical score. You can view other people's achievements to make sure you stack up well, or if you're possibly outgunned.
5) If you have a Windows Media Center PC (which I do), you can stream audio, video, and pics (plus TV and Radio if you have the right capture card in your PC). Only downside is it won't play DivX files, but it will play most other stuff, including DVD's in your PC's drive. No stuttering. Very nice.
There's other little stuff, like automatic updates for backwards-compatibility with older Xbox 1 games (which some are still buggy), and built-in testing for network connections, not to mention MicroSquish's greedy way of paying for extra little games from Xbox Live.
But all in all, I love this friggin thing.