I was feeling pretty proud of myself for planning a complicated month-long trip to Europe--planes, trains and ferries, from Helsinki to Edinburgh. Then I actually looked at my Icelandair Fort Lauderdale--Brussels ticket and saw I had my wife and I flying in to Ronald Reagan Airport in Washington DC around rush hour(s), but flying out 5 hours later from Dulles, which is c. 30 miles away. This transfer might be possible in time for an international flight, but it also might not be, as anyone who has experienced DC traffic knows. But no matter what, it would be a nightmarish way to begin what is supposed to be an enjoyable trip.
It took my wife and I about 1 second to decide to cancel the Fort Lauderdale--Ronald Reagan Airport leg of the trip with Icelandair, thus eating the $222 fare, and rebook with another carrier for a direct flight to Dulles. Of course what I should have done was create a ticket originating in DC, but still returning to Fort Lauderdale, to avoid the problem.
So the moral for persons connecting in a city with more than one airport is: Don't assume your airline has you connecting from the same airport. Apparently a good way to determine this is to examine your ticket before you click "pay" :-)