I noticed that the seat back entertainment systems on Delta Airlines run Linux on a flight last week during a reboot. Heres a few snaps:

It’s reported that Delta is running an enterprise version of Red Hat but there are no confirmed sources.

The entertainment system is called Song, which allows you to do some of the following:

• Digitally-streamed MP3 programming that allows customers to create individual play lists during their flights;
• Downloadable, pay-per-view movie programming available on demand, featuring a wide-range of current offerings for all ages;
• Interactive iXplor moving map program with zoom capabilities and points of interest information; and
• Connecting gate information broadcast directly to personal in-seat video monitors.

Engadget has a nice article detailing the system from 2004.