The book is a very nicely written argument that US copyright laws should not be treated like property laws — that owners of copyright should not be able to hold power over copyrights for eternity. Lessig suggests that releasing copyrighted things into the public domain after a reasonable time is key to culture staying creative by building on what has come before.
What's interesting about the book is, it's being released, like Cory Doctorow's novels, for free download. So, Lawrence is putting his money where his mouth is, indeed. :-)
Because Larry has released his book with a Creative Commons license, others have already created multiple format versions of the book (iSilo, Mobipocket, MS Reader, Plaintext, etc. and another in Plucker format, all for free download.
I'm am now at page 130 and I must say Lawrence has a great style of presentation, using stories and examples rather than getting bogged down in lawyerly mumbo-jumbo. In fact, I'm enjoying the read very much. It's got me thinking about copyright, ideas and creativity in a way I hadn't before. That's good, especially as a creative person working in the Internet realm.
If you have interest in this area, I can recommend Free Culture quite highly, even though I'm just 1/3 the way through it. The flow of the book is very good, the structure of the argument is logical (but mot unapproachable) and it's an enjoyable read that makes you think. Can't beat that!
Update 2004-03-29: Now you can hear the book as MP3s read by various folks. Pretty cool.