I get burn out a lot. I've made lots of progress lately, having planned and written another dozen rooms since the last 11 done last week. But it gets slowed down when I have to Photoshop the map to reflect necessary changes due to the writing, and when I have to correct conceptual errors which inevitably creep in from time to time. This week has been particularly trying, as I've been writing notes on paper at work and now have 30 pages of hand-written notes to convert to Word format. And they're in about as much order as one could expect from the Mad Mage!
But I've been running into burn out. Not burn out as in not being excited by it or having writer's block. I'm possibly more excited than ever. Each room is a step closer to the summit of Mt. Everest!
It's just the sheer magnitude...
"Ok, how do I make this room unique and interesting compared to the previous 199 rooms I just wrote?"
It's also a problem with finding enough monsters to logically fit the areas and rooms. I have a list-sheet of every new magic item, every monster, and every new spell used, plus a list of all the monsters (published ones) that I've used to I don't over-use any. Granted, some will appear in more than one room - that's not a problem. But sometimes it's just overwhelming trying to come up with a unique trap, mystery, or monster.
"Hmmm...what could be lurking here? A lich? No, he'd be too powerful for this area. Plus, there's a lich across the hall on the other side of the passage. A purple worm? Too big. Vampires? No, hordes of vampires are silly. Some orcs? Not on Level 8. They wouldn't last 5 minutes, against either the monsters on the level itself or the PCs...no challenge there."
So yeah, it's getting to the point where I want to finish this because it's almost as if I see all these rooms still needing writing and I'm going - "WTF? How am I gonna detail these rooms?" Plus, some rooms are "complexes", ie Room #21A - #21G. That ain't one room folks, that's 7 rooms.
Some of the complexes on Level 8 are just insane. Room #37 looks cool, but it goes from #37A to #37L - it's actually 12 rooms. And I mean 12 rooms, not a main room with 11 small 10' x 10' closets.
On Level 8, I had Rooms #20A - 20H, and I'm writing up a storm. Then I realize that one section really is isolated and needs to be its own sub-letter/area. Plus, I had monsters I wanted to use that fit there better than anywhere else. So I had to add Room #21I. But...in order to do that I had to Photoshop the maps because otherwise Room #21I was way out of place (rooms flow in a logical pattern on the map). Ugh!
I swear, if WOTC sees this one day when the Bunker Pricks "tattle" on me
, and if they offer me $50,000 for it, I think that would come out to less than minimum wage, counting how many hours I'm putting in! 
). It will all be worth it when it's done.