found a paper with a description of an analytical skylight system:
http://www.cs.utah.edu/vissim/papers/sunsky/sunsky.pdf
would be nice to see something similar in vray one day 
-oconv
yes 
i third this
Tom
Yes please.
--Jon
yes yes yes…I hope also!
well its maxwells phsyical sky and it has been talked before…I think this for real will come after 1.5 but, I think its essential for any gi renderer.