MaxKaladin, good stuff.

I might have to yoink your idea.
There's some good thoughts here.
To T. Foster, yes, the book is worth it IMO. The first third that's intended for players can be a little goofy, but the DM stuff is excellent. I wouldn't go so far to say that it "advocates" the big campaign dungeon. It simply advocates dungeons in general, and gives a couple ideas for some really weird ones. Though there is some info good for explaining the mega-dungeon as well.
One thing I found interesting is the encounter building part. It actually suggests that when you draw up an encounter, you actually draw the room last. You start with a focus opponent that fills one of about 6 or 7 different roles. ie: brute, blocker, freezer, and my favorite, the hoser. (I pictured a troll wearing a tuque going "uh...how's it goin, eh?")
So you pick your focus creature, then imagine how an average party would deal with it (an average party, not YOUR party...that'd be cheating) You then pick a couple ways to defend the focus, then draw the room around it last, because you'd assume that the focus opponent would pick a spot most advantageous to it.
So what this book
really advocates is making encounters first. Then you put them together in interesting ways, then you explain them. Rather than the old method of drawing out a big huge map first and then filling it with monsters and traps. (the traditional way most of us have been doing it)
This change in design focus, while interesting, can be good AND bad. I have to say I just picked up Barrow of the Forgotten King and have never seen such a scattershot group of opponents in a module, ever. So, "tactical first" can lend itself to that too...so watch your step. IMO, you still have to have SOME rationale. I couldn't run a dungeon without at least considering its origins. Not for me anyway.
An aside...to those of you who've read the reviews on Barrow and said to themselves "well, there's no way it can be THAT linear." : Yes, it can.
Anyway, some nifty ideas here. I've got a big dungeon a-brewing in my brain now.
Great discussion!