You guys probably know about this, but if nodes become a circle (i.e. if you start at one node and trace the outputs you will eventually find yourself back at the starting node) or simply if the output of one node leads to an input of the same node, Terragen will crash. Yeah, I know most people won't go "Oh, I wonder what happens if you connect this here to make it a circle - oh crap I just lost all my work," but with a lot of nodes in a small space, an accident can happen where you didn't mean to set that as the output location and there will be a crash. The same could happen if you forget that constant scalar 06 goes with multiply scalar 04 and not constant scalar 09 - boom crash.
I'm just saying that it would be a good idea to have a "no outpu" check. That way, if the node connection will cauase a circle, then a dialog box could come up and say "Illegal output - would cause node structure to be unstable/have no ouput/etc.." and it won't allow the connection. Or just have the line red and not allow a connection - just in case.