I figured I'd put together some of the research I've been doing, so I whipped up a quick image to see how it turned out.
I am not impressed with how "flat" the foliage came out, and this was most likely due to the soft shadows AND diffuse lighting all in one. I need to watch that next time.
Additionally, I need to re-tweak the foliage shaders so they work better in darker, more diffuse scenes. (this applies to the foliage I shared - the translucency and luminosity is likely too high, so keep this in mind if you use them for a darker scene).
The clouds came out as planned, and I used a distance shader with more cloud layers to keep them hugging the mountains.
The surface/ground shaders are 2 fractal stacks (actually HUGE groups) but gave the ground much needed variation. One for dirt, and one for foliage ground. The snow is 2 layers, one with slabs of built up snow, and another with a thin "dusting" layer. This seems to give pretty realistic results.
For the foliage itself, I used atleast 5 models, and used a variation method similar to the one in the foliage I shared. This kept them more "clumped" and realistic, though still more work to do.
The castle was assembled in Google Sketchup. I'm starting to like this app more and more (hated it at first, but it was the best structure modeller out there for free).
There will be a model on the road of a horseman, possibly with a carriage, but I don't have those models at the moment.
Stats:
rendered on 2 cores @ about 20 hours per core.
minor color/contrast/sharpening in Photoshop.
detail 0.8, AA 10
Thanks for viewing.