I'll always remember a certain radio exchange that occurred one day as Walt and I were screaming across southern California 13 miles high.  We were monitoring various radio transmissions from other aircraft as we enter Los Angeles Center's airspace.  Though they didn't really control us, they did monitor our movement across their scope.  I heard a Cessna ask for a readout of its groundspeed.  "90 knots", Center replied.  Moments later a Twin Beech required the same.  "120 knots", Center answered.  We weren't the only one proud of our speed that day as almost instantly an F-18 smugly transmitted, "Ah, Center, Dusty 52 requests groundspeed readout".  There was a slight pause.  "525 knots on the ground, Dusty".  Another silent pause.  As I was thinking to myself how ripe a situation this was, I heard the familiar click of a radio transmission coming from my back-seater.  It was at that precise moment I realized Walt and I had become a real crew, for we were both thinking in unison.  "Center, Aspen 20, you got a groundspeed readout for us?"  There was a longer than normal pause.  "Aspen, I show one thousand seven hundred forty-two knots."  No further inquiries were heard on that frequency.