I have about a dozen notebooks full of detailed discriptions and drawings of maps, monsters, NPC's, puzzles, tricks, and story lines for mods for Quake, Thief, Deus Ex, NOLF, Doom 3 and stand alone TC's.
I also have dozens of prototyped maps and models on my hard drive.
As compulsive as that sounds I really sift through my material patiently until things comes together in interesting ways.
edited: Just noticed that this is in the coding section, so related to code documentation specifically -- errr - awkward
