UA_Flyer: well-stated! We live 10 miles/15 minutes from Dulles and ONLY travel from there. It's a $30 cab ride vs. $90 to the airport. With the new Silver line extension, that'd be a 15 mile ride versus > 1 hr to DCA. For domestic travel we have access to 2 Star Alliance Lounges (Turkish and Lufthansa) and several more via Priority Pass versus a couple of restaurant options at DCA.

Not to mention that I feel much more comfortable (as a former light plane pilot) with the length and normal approach and departures from IAD.