Yes, I used it to fill the voids in my old west butte (
http://leadadventureforum.com/index.php?topic=105875.msg1428457#msg1428457 and while I was doing that I noticed that odd blobs dried in an interesting form, so I played around with it. On the butte I carved the excess off, but on the sci-fi hills I basically just blew the foam inside itself and let it mushroom up.
I use the foam with a gun, not the stuff that comes in a can, as it's easier to control. If you get it too high it will fall over, but I'm going to do some more with formers (cardboard tubes) to see what they turn out like. It very light when cured but not too strong, but I think it'll stand the rigours of the tabletop.