Floating houses (Warning: Pet peeve) in mountainous terrain in sims is pretty much the most common thing ever. Years ago I proposed making all houses have "sub basements", which meant essentially containing structure that went down maybe about three floors below ground level so that when a house found itself on a steep slope, it would not end up hanging in the air, defying gravity.
Microsoft Flight apparently had the same idea, and is the only sim I know that ran with the concept, ending the issue of dangling houses. I proposed it here again a long time ago as Aerofly was a new sim at the time and it seemed a good idea to implement such a concept at the very beginning, but again the idea was lost (sigh)
Maybe the concept will have its day, on some sim or the other.
[Blocked Image: http://imagizer.imageshack.com/img924/3373/8IS8Rj.jpg]