I agree dark fire I think playinf in space can be helpful to those who are new to terragen or (like me) node based programs in genral.
Also I was wondering how you could apply the crader shader to the planet shade effectivly, for example in the thread Fun with the crater shader you 3Dguy seemed to get some pretty cool resualts out of the crater shading and even things resembling tital waves. I'm now wondering wether you could use it to make a nice looking meteor impact, like the ones you always see on the science channel speicals about the end of the dinosuars.