Flight wide failure of the IFE from experience has been quite common, although the cabin crew often get it "rebooted" and working. Thus it would be wise to have books / laptops /ipods etc as a backup. Given the content of the IFE, I generally end up listening to music and watching the in flight navigation.
In 2007 I returned from Vienna in J with Austrian airlines and the sound to our two seats did not work. we each received a EUR35 duty free voucher which was a more tangible benefit that a travel voucher, as Austrian stopped flying KUL-SYD shortly afterwards.
In 2007 I returned from Vienna in J with Austrian airlines and the sound to our two seats did not work. we each received a EUR35 duty free voucher which was a more tangible benefit that a travel voucher, as Austrian stopped flying KUL-SYD shortly afterwards.