I never saw anyone here bring this up, so hopefully it's not repetitive.

Apparently spies can use another civ's airport. Twice I transported my spy back to one of my cities. I wonder if this counts against the "airlift one unit" for the AI. I did not have open borders (or good relations) with the civ either. I'm curious to try if this works for all units during open borders.

http://img71.imageshack.us/img71/1524/civivspyplane7qd.th.jpg (http://img71.imageshack.us/my.php?image=civivspyplane7qd.jpg)