Hmmm..  I didn't even think of using the snow shader.  That should be pretty cool.  Thanks for the idea.  I wish you could have a single shader that randomized as a procedural for every instance.  The best you can do that I have found is to set the scale really small and set it to world instead of local.  But it still doesn't look all that great.  The snow should be interesting, I will let you know how it looks.