We just returned from Hawaii over Christmas with out 7 month old. Fortunately for all she was VERY well behaved. On the trip out from DFW-HNL on Delta, we were unable to upgrade but the gate agent gave us the center row of five seats in the L-1011. We were able to put up the armrests and let her crawl over the seats during the 8 hour trip. No crying, and a very happy baby. We got a lot of dirty looks from other passengers as we boarded with the baby, as I think they assumed she would be a problem, but after about 5 hours into the trip they were coming over to visit with her, smiling and talking to her. I guess she proved she could be a good little passenger.
On the return we flew back in First, and at the beginning of the flight the FAs were just short of rude to us, taking our meal request last, never coming to check on us. But again, as she stayed quiet, slept most of the trip the FAs warmed up to us and to her.
There is a bias against infants on flights from Flight Attendants. I never believed it before, but after seeing the change after travelling with (fortunately) a well behaved baby.
My advice to anyone travelling with a little one is to bring plenty of things to occupy them, so they don't get annoying to other passengers. Take as direct a flight as you can, it might cost more but you want to keep the little one happy, and several connections with possibly delays don't add to a happy travel experience of an infant. Also try to travel at times the baby will be at his/her best. Should you really take that 5 AM flight, or the redeye? Sometimes you don't have a choice, but when you do think about the little one's schedule.
As a very frequent flyer and being around screaming children, I vowed never to be "one of those parents" who ignore the screaming. I know there was some luck our 7 month was so well behaved, as sometimes little ones get cranky, just like 30 year olds, 40 year olds and 50 year olds who fly, but you need to do everything you can to make the flight pleasant. You don't need any more stress crammed into that little overfilled jet.