Thanks both for the replies. Frapos, I actually am looking at carriers other than ZED, ie Northwest, Continental, etc. However, at my airline you can buy these passes on the spot, wheras you need to apply for ZED passes a week or two in advance, which is why I'm interested in figuring out in advance how ZED works in the "real world."

It sounds like both of you agree that different airports within the same mileage zone is OK. That's good to know. I guess the question that there's likely to be the most confusion on is whether I can fly LAX-LHR on BA or Virgin when I have a ZED ticket for LAX-LHR on AA. It sounds like OSflyer is saying "yes," but it'll all depend on how each airline's ticketing staff interpreted it.

Anybody else had experience with this?