Almost Human's Antti has treated us to a nearly nine-minute "sneak peek" of the dungeon editor they're preparing for Legend of Grimrock, and it looks like it's going to be about as user-friendly as anyone could have imagined. Changing the dungeon wall set, adding objects and monsters, linking keys and fireballs to doors, and advanced scripting are all briefly covered:
I really hope this is extremely popular - I could use some more Grimrock in my video game diet.