I've had the PDF version of the version of this book for some time, but I found myself using it so often that I decided to buy the hardback. It is quite simply the most useful idea generator I have on my desk. If you're a DM I highly recommend you pickup a copy. If you make up a lot of dungeons it's a must. It will keep your ideas fresh and surprising for your players.
If you've got a game in 2 days and don't have anything generated simply read through some of the charts. It will seed you with a dozen stories in no time. I'm a busy guy with a full time job and children so this book has become as important as my DMG.
I highly recommend the hardback as well, it's got a quality binding and frankly the paper is a better quality that the current WotC books.