Read online for free, or buy it. While written with an eye towards the development of online applications, this book can easily apply to almost anything in business.
A follow up to Wendy's previous tag, another take on Google Wave from more of a layman's point of view (a writer). Plus, it includes the video presentation right at the top. Well worth watching.
This site does a good job of showing what this application is about. The little "demo" at the top tells the story very well, as do the examples further down the page.