I'm reading this book right now. While there will be a few small things here and there that are out of date (like Pluto's status) the majority of the book covers the history of how we know these things. So all the information about Percevil Lowell, Pluto's moon, Clyde Tombaugh, and all other things surrounding the Pluto story will still be correct and informative. Don't hesitate to pick this book up just because there may be a few tiny new things that have happened in the few years since the book was published.
Someone will be doing themselves a disservice by not reading the book just because a few major events have happened. The Pluto thing most people know about. He also talks about earthquakes and tsunamis, which we should all know has changed a bit since 2003. In other words, anything that is out of date should be common knowledge so there isn't much danger in being tricked. None of that makes the rest rest of the information irrelevant.