I've been paging through the DMG myself, and the content seems pretty worthwhile. I've been DM'ing for 11 years now, but I read the chapters on running the game and running encounters, and they were moderately interesting. The DM toolbox, however, is excellent. I enjoyed drawing up a dungeon map using the dungeon generator, and the encounter generator looks pretty engaging, too.
The book may be aimed at newer DMs, but that's not a bad thing, in my mind. There's still enough in there for an experienced DM to get something from it.