Apropos of nothing at all, I found this tidbit of information oddly compelling:  there are only five airlines which fly to all six continents (scheduled airline service to Antarctica being essentially nonexistent):  Emirates, Air France, British Airways, Malaysia Airlines and South African Airways.  (Emirates is especially notable -- with their recent addition of Dubai-São Paulo service, they're the only airline to serve six continents with one hub.)

There hasn't been a US airline in the club since the demise of Pan Am, but Continental could be in if they add service to Africa, or Delta could make it in if they add service to Australia/Oceania.

(All of the above info courtesy of Patrick Smith's consistently fascinating "Ask The Pilot" column on Salon.)