To those who are interested in modelling heightfield and/or GPGPU techniques: I just released the free binary and all of the source code for the Scape terrain editor prototype at www.decarpentier.nl/scape. Scape allows the user to 'paint' complex and natural looking terrain in real-time by using the GPU to not only render but also to edit the heightfield using both common and novel procedural algorithms,
The GUI still needs some work (some things don't seem to work properly, and some don't seem to work at all, all the brush icons are the same, etc.), and I can't seem to figure out how to properly navigate or use a pen of a different size, or how to set some parameters of the terrain...
for a prototype it's quite amazing. Especially with its high-res realtime terrain shaping abilities (and realtime really means -- real -- time -- ) this is one of the most stunning tools I've seen (way better than e.g. WorldMachine for which I've paid some real money).
Btw, I totally agree with you on the menu side. That's far from polished. But the navigation and radius controls are actually quite user-friendly, if you know the right buttons. Be sure to check the userguide under the /Docs folder on this one. And if you really don't like the default keyboard/mouse mapping, you can customize it by editing /Bin/Settings/ButtonDefinitions.xml as well.