I bought this book to read with my 9 year old son. I read it through first as I had read a number of reviews which said it was a little too informative in places.
I thought the book handles most topics very well and used the book to discuss a number of issues with my son. He is moving schools in September and, even if he doesn't start puberty soon, some of his friends will so we have been talking about what he should expect. the diagrams were very useful for explaining the biology behind it although I could have lived without the erection page and description of sex. Having said that, he has seen more graphic sex scenes on wildlife programs and I have no problem discussing those with him so my aversion to those pages is likely to be a result of my own reticence over raising these issues with my child.
I would consider this (or the girl's version) a must buy for all parents - even if you don't use it with your child, it will help you to form ideas of what to include and how to phrase these ideas so that your child understands what you are saying.