I would guess there's customs to enter Spain just like we have to go through customs at PC to re-enter USA. Then customs again at airport maybe? I don't remember. The last time I flew home from MX was way before 9/11. I know for sure there will be customs to go through when we arrive back in US. Also if you will be connecting, you need to go through customs at the first city you arrive in the US. We did this when we flew home from Ireland; we stopped in Boston so went through customs there, then connected to Philly. When we flew home from our Alaskan cruise we had an 11:15 am flight and still had plenty of time. Even took DCL transfers but also did onboard check in so we didn't have to check luggage. That saves a lot of time. Hopefully we at least have time to grab a snack in BCN.