the three sites I have done for small airlines since I was working full time in IT have all been Linux desktops.
Its saves a bloody fortune on licensing and if you ever get a visit for software they just turn round and walk out the door when they find out what you are using.
The users I must admit hate it with a passion mainly because they can't screw around with it and its not windows and the burds have issues with not having office and using openoffice instead. But the boss quite quickly likes it after zero down time and no money for licenses going out. Its a hellva lot more stable network to run without needing all the back office staff that MS requires. once its set up 30 mins a week does for the house work. I just had a sudo script for creating users that HR used if they had a new start. 30sec after walking in the door everything was good to go from email through to FTL's.