I hacked together something today, a terrain drawer with the JS terrain api. Most probably the first in a series of vids, but this is what I have so far: http://www.youtube.com/watch?v=jPpJvv5ZTzc
I'll most probably abstract it a bit, give it an on/off switch, and a variable block size, and then see if I can make it auto smooth, which will be really awesome