The top five are Los Angeles, Hartsfield-Jackson Atlanta, Chicago O'Hare, San Francisco, and Dallas/Fort Worth.
But the five busiest airports around the world (January-July 2011 figures) are Hartsfield-Jackson Atlanta, Beijing Capital, London Heathrow, Chicago O'Hare, and Los Angeles. Dallas/Fort Worth is number eight, and San Francisco number 22.
San Francisco is easily explained by the importance of the tech industry to the city and its surrounding areas.
If we discount Beijing as it is reportedly difficult to access Facebook in China and there are local services addressing the local market, the next busiest candidate is Paris Charles de Gaulle. But Facebook penetration is fairly low in France, where there is roughly one Facebook account for every four people, around half of the Australian figures.
Sydney punches above its weight in Facebook terms, coming in at number seven on the 'most social airports' list thanks to the high per-capita passenger count and Facebook penetration.
Facebook also noted the peaks that occurred over the Christmas/New Year period in 2010, specifically on December 18 (the Saturday before Christmas Day), 23, 24, 29, 30 and 31. December 18 saw a peak that was twenty times the normal average.
And that might provide a clue: could it be that people are much more likely to 'check in' at an airport when they're travelling to meet family and friends compared with business travel? That would help explain why Las Vegas McCarran airport was number nine on the Facebook list but 18th in terms of passenger movements. Similarly, Miami was 12th on Facebook but 24th for busy-ness.
But why would you bother publicising your presence at an airport at all? Surely it's better to keep the fact that you're away from home to as small a circle as possible.