Heading Out is a must read on this subject tonight, with some very helpful background.
In an aside, I was on the phone to my Dad in the U.K. this morning, and I was asking if any real economic consequences have surfaced yet. It's a pretty interesting natural experiment in how dependent modern economies are on air travel - Europe has now effectively had air transport altogether withdrawn for several days with no warning.
He said so far the only visible consequence for the person in the street was that the supermarkets had run out of lettuce. I forgot to ask if there had been panic buying of lettuce :-) Of course, the airlines are losing $200m/day, and I wonder if a couple will go under if this goes on for a long time, since they weren't in great shape even before this.
Update: Wow. Guardian says 30% of UK exports travel by air, with pharmaceuticals particularly reliant. That sounds like it would start to bite pretty fast.