After vowing to never buy another video game system ever again after dumping more money than I care to even think about into the Dreamcast a few years ago and before that into the cutting edge 3DO I finally broke down and bought an Xbox.
Why did I buy an Xbox then?
Mod Chips. The Xbox has proven to be one of the most modifiable consoles out there. For not a lot of money I can get a mod chip that snaps onto the board and replace the hard drive with a whopper 200G drive and instantly I've got a really fun, media center type PC.
You can FTP files to it, it can play music, photos, videos off of your network. You can copy entire movies to it, even entire Xbox games. How cool!
I just got the unit last night and am getting myself a mod chip now so I can rig it up with everything that I want. Out of the box it's not all that exciting. Homebrew apps on your Xbox -- very fun!