:-) Many thanks tilt! Sorry for being away since days, I'm very busy being back to work after Christmas vacation but I'm definitively not idle. I'm planning about experimenting the most I can, than put it all together to create some sort of "porting" of Saderan techniques for GIMP. Since Saderan makes heavy use of PS tools not available to GIMP (such as dynamic layer styles or adjustment layer, and such) instead of simply trying to fake them I think the whole process should be reworked so that GIMP and it's inner mechanics are leveraged to achieve comparable results.
The weak point in pretty all tutorial I've read so far is that they are created over the "Do this, and this, and this!" model, that doesn't require you to really mind what you're doing. You find yourself blindly following instructions, trying to understand what should happen... I think that a more "describing" approach could pay a lot more. Something like "We will emulate real mountains and relieves as they appear on a aerial photo, so let's look at what we want to achieve, THEN let's make an example of how to get things done in GIMP/PS". Single step would be "Since <reason/observation> we need <result> so that <benefit>. We achieve this through <operation(s)>." so that every step is supported by reasoning and everyone could feel comfortable in changing things at his own will.
Maybe I'm wrong and I "think too much" :-) but I'd like to try this structure and see what it brings.
Anycase, I still have to learn a lot! :-P