A friend coming back to the US from Europe this weekend snapped this photo for me on an Airbus 330 FinAir flight from Helsinki to JFK which shows the seat back monitors obviously booting Linux. It looks a lot like the RED Entertainment system which is a custom program running on top of Linux that Virgin America came out with sometime in 2007 and is discussed a bit on engadget. He's pretty sure he saw the text "RED boot" flash by at some point. According to my friend, its a touch screen with an optional seat control module which is used to display "Movies, Documentaries, or (pre-recorded) TV programs, Games, or Audio programs on demand, serve as a Flight map and flight parameters monitor, provide Front and down cameras view, Shopping on board, and Telephone and text messaging services (with use of Credit Card terminal)". One internet source I found suggested that "most inflight entertainment systems run Linux and have been doing so for the last 7 or so years". Some makers include Panasonic Avionics and Thales Avionics.
update Aug, 2011: more pics added from recent Finnair Airbus 330 Reg OH-LTS flight AY005 Helsinki to JFK