Thank you all! Hi calico, I've been busy for a while, and happy to be here now!
@sonhine777: The trees are all Xfrog models: Aesculum hippocastanum, Picea abies and Picea pungens. They all have snow applied as a surface layer in their internal network. It's the same shader I used for the scene and it's slope constrained, with the 'use Y for slope' option activated and set to 'Planet/Object normal'. In this mode you can place the snow only in the superior part of the branches and foliage giving a very realistic effect. You can modulate the amount changing the maximum slope value. The snow is also a little embossed to give some thickness, but with external objects you have to maintain very low displacement values or the geometry will explode.
The bended tree in the foreground required some little more work to do. I wanted to give the impression of a tree "overcarried" with snow, so I created the model in MAX modeling some "fake" snow block on it, then I've inserted it with precision in the scene using the LWO exporter, wich is EXTREMELY useful. I've never used the LWO exporter before and I discovered that it's not so tricky as it can seem (I've found somewhere over the board a very clear explanation made by Oshyan on how to use it) and it's a really powerful instrument for integrating models and geometry from 3rd party applications
The rock conglomerate and the ice blocks are all fake stones with a redirect shader, applied over a strata terrain after lots of experiments
I wanted to render the overall mood of an overcast day without direct illumination. I've hidden the sun with a 3d cumulus layer and overexposed the camera. I also thought about a lightdome, but I'm afraid it would require an eternity in terms of rendertime..
Scene rendered with ambient occlusion, detail 1, antialias 3, GI and GI sample quality set to 3 – approx 16 hours @ 1000x750