I though that since I am now in Hong Kong and have been using this book I might give a bit of an update of how I have found it, and I must say that it is very useful. Okay, I am also using it in conjunction with my smart phone (I managed to get a sim card that gives me internet over here, so that is also very helpful – you can purchase them at the airport, and the same was the case when I arrived in Bangkok). I have taken a couple of the walks that they suggested, one through the Kowloon Markets (and it is quite extensive since it starts at the Bird Market and finishes at the south end of the Night Market). Mind you, the problem with the market walk is that the Bird Market begins to close down when the Night Market opens up.
The book is very thorough, though I must say that the way they price their restaurants is a little dicey. I suspect it is because they are only listing good restaurants, but there are hundreds of little hole in the wall restaurants in Kowloon which are even cheaper than what you would get in the book. For instance, you can have a pretty decent feed for around $6.50 US (though remember that the Hong Kong Dollar is pegged to the US Dollar so the prices are not going to change based on the exchange rate, which does affect me since most of my capital is in Australian dollars).
I guess the best way to use this book is to read it through before you actually go to Hong Kong (and this will apply to any of the Lonely Planet Guidebooks) and make a note of what interests you and then plan your days around those particular sights. Remember Hong Kong is actually quite a small place so you can fit a number of things into a day, but don't go running all over the place, try to localise all of your activities. Mind you, because it is also a small place, you can quickly run out of things to do (unless you are simply interested in shopping and having fun, then that can last a lot longer). I've spent a week here now and you could say that I am pretty Hong Konged out, though I still love the place.