Gaaah!

Oh, sorry about that, getting slightly frustrated with my lack of ability here. So much input to parse. I can see what you mean about the rivers being too fat, and I guess it'd be nice if they'd start further up in the mountains... not sure about that, though.

I did manage to do something that I think could eventually resemble the tutorial you mentioned, but the Gimp severely lacks layer effects, so there's this whole manual process involved (copy layer, make a bump map that matches the layer mask, applying that bump map, delete layer copy and start over if you want to change the layer mask - best I could find so far ) - And nothing to show for it for now... bleh.