When developing my entry to 2nd PGD mini competiotion (which was never finished) I have been fidling with procedural content generation quite a lot.
Amongst other things I tried generating clouds using "Perlin noise" and even got some nice results. But the problem was that then I tried rendering that texture to sphere it got disturbed due the way how spherical texture projection works so in the end it almost looked ugly.
I should probably have used several smaller textures and then projecting each of them to the sphere so the distorition would me much lower.
Anywhay procedural texture generation development is currently on hold as I first need to design a way to make nice game GUI in an easy manner.