@falagard: I currently have some plans for the clouds
I will first focus on the high layered clouds as mentioned above, as they're much more simple to simulate. The colour lookup image will be the same as the sky and the sun colour. Think I just need to pick a few colours: Sky scattering, sun colour, backlight... and all those are already in the lookup maps. As for the cloud generation, I've in mind a simple shader algorythm to generate the clouds in a small bitmap (covering the whole sky) and then giving it texture with some special maps
About dynamic lighting, I also have some ideas.
Billboard clouds will come later
@BRAINLESS: I thought the pow operation was implemented in cg. Anyways, downloading the latest cg toolkit and replacing your current one should work, and else you can always remove the pow() call in the shader. All will happen is that the glow effect will be larger than expected
About the resource group, it was an early design decission. All that Caelum creates and manages, should be in Caelum
@jacmoe: Caelum in latin means "sky", so expect a lot of functionality for everything sky-related in my plans for Caelum