I have found it easy to hold the carrier after the captain announces to 'be seated for take off/arrival' Once they are seated they can't see a thing.
Continental doesn't give me any kind of ticket saying pet on board, etc. The only time I had to take Mr. Big out was thru the security check in and even then, not one person asked for proof. And this was just a year ago mind you; not before 9/11. I have already purchased Abby's ticket and I don't even print out anything for that. Just my boarding pass.