Post feedback as issues here on Github for the Aurelia book. Be as descriptive and honest as you like.
If you are interested in buying the work in progress Aurelia book, you can get it here on Leanpub for currently as low as $12.
At present, the book is in a raw state. As such, you will encounter numerous spelling and grammatical errors. If you do encounter any, please do not hesitate to let me know. There will be proofreading and edits made to the book towards the end, but if we can catch issues early, that is the best approach.
If you have any ideas for subject content in the book, definitely let me know. This book is for the Aurelia community, I want this book to contain answers to questions you have, talk about aspects you are confused about or elaborate on parts of the official documentation.