It's an odd beast, that's for sure. Chapter 1 is useful if you're a n00b DM, or if you're interested in pop psychology. It's actually stuff that I think should be in the original DMG. Chapter 2 is filled with totally random usefulness, from traps (which are all pretty good) to locations (which every DM can make use of, combine, and alter endlessly), encounter tables (which can be meh, but are always fun for me). The mobs and the treasure hoards aren't that great -- mobs are a bit too generic, while hoards seem a little half-hearted, like they were just filling up some spare pages. Chapter 3 has stuff that, again, I think would be useful in the core DMG about campaign design, though the notes about medieval history seem pretty pointless (and MMS does it with infinitely more flare). The trade and job notes seem pretty superfluous to me (do we really need to know how many cobblers vs. coopers there are in a given town?), the crme and punishment section is iffy (it ignores magic pretty rigidly), while the Magic Events from Chapter 3 are pretty neat little campaigns-in-a-page. Chapter 4, IMHO, is entirely disposable, but it could be useful for accessing quick NPC's. Chapter 5 works well with the complex NPC's, though contacts and hirelings probably don't need the pages they're given. Chapter 6 has Students and Mentors wich is interesting, but a lot of rules for very little rewards. Much like Running a Business, it takes things that are boring and glossed over and gives you rules for them. The Teamwork Benefits and Companion Spirit ideas are interesting, but they don't seem like much more than power creep for no real reason. The Prestige Class info is, again, stuff that should've been core. Organizations are transparant plot hooks, and guilds are, again, stuff that is usually glossed over. Chapter 7 is worth it's page count, because it gives some new ways to do magic items.
So in summarry? DMGII contains three things: A lot of stuff that should have been in the core DMG, a lot of stuff that adds rules and rolls to the boring aspects of the game (

), a handful of useful references, and a few interesting ideas underneath.
Worth $40? I'd say no. I'm glad they took a risk with it, but it's just kind of a hodge-podge of ideas. Blech.