We've brought the carseats for our two sons (now 4 1/2 and almost 2) every time we've flown with them. Yes, it can be a real pain to install them, especially ona full flight when people are all trying to get their own seats. But, it was very mich worth it to have them, as we could then install them in the rental and know that they were the same ones we are used to using. We tend to take advantage of preboarding so we can get a jump on the restof the crowd. When we flew Southwest a couple of weeks ago, we were told that the carseat had to be in the window seat, which was new to us. We basically had to seat two of us on each side of the plane, leaving the aisle open. On the way down, it was a full flight, but the people seated next to us were very kind about being near kids (I think it helped that the boys were very well behaved). On the way home, the flight was very empty, so we were able to have the aisle open. I guess the reason I mention the window seat thing is cause it made me wonder what would happen if you were flying alone with 2 kids in carseats. Someone would have to be away from the others then?