Indeed the first chapter is tough - we learned that through various iterations with many reviewers. Eventually we decided to just introduce you and skip the meta talk about methods and stuff. That should be in the "Welcome" passage before the actual chapter (included in chapter 1 - free download). If you didn't find the argument to let you know whether or not the book is for you we might have to refine this section and bring out our main points more.
Personally I am not convinced a starting chapter that told you how the book is going to teach you things would help that much with deciding whether you'd be comfortable with said book. It might be much more helpful to have a more advanced chapter as a free read oftentimes.
Eventually Meteor in Action will be a printed book as well, so that theoretically you will be able to browse through all chapters in a book store of your choice. Always assuming they carry Manning book, of course :)
Jump in faster I say.
Site is extremely well done. Is that something advocated by Manning or a personal thing?
This would solve what buyer wants without giving all your content away
However, I'm not sure the first chapter is going to be your main selling point to end users. It's the introductory chapter, that goes over the history of Meteor, and what Meteor is. That's not the chapter that will sell me on a new book, I don't know yet how you intend to teach different programming concepts, or how you introduce how to actually use the framework. It might be of more interest to people if it was the second chapter maybe?
I'm interested, but not quite sold yet personally.