My wife and I figured out a great "trick" with our kid when we have a seat for him (i.e. we bought it, or the one time we got lucky at checkin with our carseat). I "pre-board" with the car seat, diaper bag, and carry on; she waits until the last possible minute to board ("final call") and by the time she gets to the seat, the carseat is strapped in, the carryons are stowed, and the diaper bag is slipped under the seat. Ba-da-boom, ba-da-bing. Easy. I'd recommend this to anyone. Keeps the kid happy (lets him run himself out a bit more), keeps the wife happy (she's not fighting the kid while I wrestle the carseat), and keeps my fellow passengers happy (no screaming kid during boarding, I don't bump into people with the heavy carseat).

The difficult issue comes up when we're delayed and I have to board with the hordes. Try getting on a plane when you're either surrounded by kettles who don't understand how to get out of the aisle when they're taking out their magazine from their rollerboard; or the DYKWIA "elite" who glares at me because I had the audacity to brush his elbow he has sticking 8 inches into the aisle with the car seat. (I have also noticed on UA, as a pathetic *S, no pre-board anyway, even with kids, so this is the usual on UA).