I think it would be cool to have unlimited, but temporary, access to the iTunes store.
Consider it. Plug in your headphones and sample everything the iStore has to offer. Free of charge, or some premium attached to the flight (first class, etc). You don't get to keep any of it, though.
There's a ton of music on the iTunes store that I'd love to listen to, but not all of it I'm willing to pay 99 cents to actually commit to buying. Here's a chance to try-before-you-buy. They could let you bookmark the songs you liked, and later when you log in from a land-line, you can purchase all those bookmarked tracks.
It's a compromise with the unlimited-subscription model, but here's a venue where it would actually be practical. You're stuck on the plane for a few hours, so here's a prime opportunity where they've captured your attention. Not charging means skirting the tax and country boundary issues. It's very short term, by definition, which limits the amount of abuse it will get. I'm sure you'll get the unscrupulous few who will bring recording devices and try to rip off the store, but in a setting where you're paying hundreds of dollars for entry (e.g. the plane ticket), all your devices are being monitored (airport security), and you're only accessing it for a few hours anyway, a lot of these concerns are mitigated.
I'd use it.
Heck, they should do the same thing at Apple Stores!