The undo function is completely useless in the toolset. It only works on a very limited number of things, so when you actually screw up and want to undo something, it undoes the last thing its allowed to, which is likely something you did like a half hour prior.
Yeah, I'm a modeller, but I think what really helps is how much I love maps. My room is covered in the maps from the various Birthright sets, Baldur's Gate 2, Grand Theft Auto, etc.
Anyway, now I'm having a problem. I edited the walkmesh and baked the level so I could walk around in it, and in game all I can see are the placeables, the terrain is gone.
The layout of the buildings and such looks way cooler in game though with all the effects.