I've started reading the 4th edition Dungeon Master's Guide. It's what you would expect, full of helpful advice cobbled from various articles about how to run a game. It calls upon theater, technology, and psychology to advise game masters how to smoothly run their games, prepare in advance and satisfy every personality type. I might be old fashioned, but I don't allow laptops and technology at the table, although the book suggests we all join the 21st Century with smartphones and gadgets.
The book is fairly fluffy without much crunch. In fact, the book has noticeably less heft than the Player's Handbook, probably due to moving the magic item section to that book. I enjoyed the poison, disease and trap revisions, but they're certainly not something you're likely to use very often. The books is less table reference and more design toolbox for creating content. Combat and conditions are thoroughly covered in the Player's Handbook, as are magic items. Experience points are clearly given by monster, regardless of party level, a very helpful change. In 3.5 I would normally consult the DMG for experience points, crunching numbers on a charts (or a Java applet). So if you travel to your game with a bag full of material, perhaps you can credit Wizards of the Coast for saving you a few pounds off your back.
I'll post more impressions as I read more.