The DM's guide sits alongside of your Player's Handbook and Monster Manual and is meant for the one guy in your group who is going to spend a lot more time thinking about your DnD campaign than you are. Still, that dude's pretty invaluable, so maybe you want to buy it for him as a Christmas gift.
As with the other books, this one is hardbound and full of fantastic art to get you into the feel of leading a group of loosely-strung-together adventurers into certain peril.
Actually, between this and listening to "The Adventure Zone" podcast, I really need to get my hands on the DnD Starter set to convince my other friends to party up. Of course, this means that I'll inevitably be the DM, so I guess it's a good idea to get this book.
