I have seen this very nice content shop at the Amsterdam airport. You can buy there different content like music, movies, ringtones and audio books and pay it with your credit card. Unfortunately, my Treo 650 was not supported, but most phones and PDA were.
I think, that to place this kind of shop at the Airport makes sense, but I doubt that people are using it. We was thinking of creating this kind of shop in Prague using a PC and a lot of different cables for all phones, but I don think this kind of shop can pay for itself. I believe that future is online downloads rather than syncing with a computer.