The fog effects are finally reality, and nice do they look! They we're first implemented using a sort of cellular automaton, but because of the development platform's restrictions it ate CPU's for breakfast..
The current fog system works using huge blended fog particles. It allows some interesting gameplay possibilities especially for the multiplayer. Hiding and camping in fog, fog removing and creation devices.. Only problem is that the fog needs to be completely deterministic, so that every player sees it the same way, but that's not really a problem as the fog system is so simple.
Among the fog there are also many other graphical improvements.
This video (with very dense fog) explains things a lot better than words would: