I think that the wiki or a few articals here would be better then a book. But i do think a book is a good idea. The only problem i see is the simple fact that there are alot of people who have interpreted the meaning of parkour differently, so by publishing a book people wil argue that the book is wrong, or that you are just tying to defend against the media's styreotype (bad guy, punk kids, graffiti, tricks ect...).
An example of this is: I was trying to get that styreotype out of my friends head. I said parkour was more then just doing flips and vaults and big drops. He countered "Well...