I just read the article by Damian Peach in the link Mike provided.
Yep, I agree that foggy nights are fantastic!!!!!
Here at Snake Valley (altitude: 490m) the seeing is amazing on a foggy night! And fortunately, the fog doesn't last long. It fogs up almost instantly like someone turned the fog switch on. When that happens, I go inside and make a cup of coffee. Come back out, fiddle with a few accessories or read Cartes du Ciel etc, and usually within the hour the fog settles down to ground level and the sky is absolutely magic!!!
Another bonus is that the fog collects any airborn particles in the lower atmosphere and drag them down to the ground as it falls.
So not only is the air calm and the seeing great, but the air is cleaner too
