This post is merely me trying to keep track of some posts that concern megadungeons that I found useful or interesting.
This one from Blood of Prokopius covers a wide range of topics and also includes FrDave's thoughts on Dwimmermount.
This one from the Dungeon of Signs is the latest of a series of posts about megadungeons. Lotta good stuff here about dungeon design.
One of these days, I need to write a post detailing how I would produce a megadungeon. Probably not too much different than some others have suggested, but it would be an interesting exercise for me to put it down.