The official Apple site about the hardware: AirPort Express
The official Apple site about AirTunes, the streaming audio software for iTunes: AirTunes
The official Apple site for unwiring your living room: Unwire Your Living Room
The official Apple site for using your AirPort Express when you travel: On The Go
The more I read about it, the better I like and the more I want one (can't seem to get one delivered tomorrow, however). I can see myself buying 1-2 for my house and one to take with me to use in hotels. Additionally, I am not particularly fond of my Linksys wireless router at home, so if the Express only turns out to work well with the AirPort Extreme, I don't think I would have much trouble convincing myself to buy one of those as well.