Just wanted to respond to a few things, as we've flow a lot over the last 2.5 years (DD took 22 flights by the time she was two).
*the airline wants you to check the carseat. Nope. Never had anyone with the airline tell me they wanted us to check the seat. In fact, we are always getting comments on how nice it is to see parents bringing the car seat on.
*the flight attendents are not happy to have to deal with you getting a bulky car seat to fit in the small airplane seats. Again, we've only ever had positive comments regarding the seat from airline employees. Flight attendants also go out of their way to assist us when necessary.
*ditto on any passengers who may be sitting near you - although in my experience, the car seat must be on the window so as not to restrict anyone getting out in case of emergency, but of course, you will be in the middle seat next to the car seat. However, the person in front of you cannot recline because the car seat and/or toddler's legs/feet are in the way. Nope. The seats always recline in front of us. Even in those little 50 person planes. If the seat were rear facing this may be an issue. Also, I always sit next to DD in the middle (as you said, they have to be in a window) so we've never been a bother to other passengers.
*actually getting you, the toddler, the carseat, the luggage, your carryons, etc. from your car to the airplane is a nightmare. If you have more than one adult, it isn't as bad - but I'd never take a car seat if I was the only adult. Been there, done that - ugh. I too did it when I was 38 weeks preggo with DD, so I can relate. Yep, it's a pain.
*almost no one takes car seats. Every time I've flown with kids, my kids are the only ones on the plane that have car seats. I have seen quite a few car seats on planes actually (I travel for business as well so tend to fly a bit). All of my IRL friends also travel w/ their car seats. I of course see as many lap babies.
Just my experience - I wanted to show the other side as well, for moms who may be on the fence about this issue. We've always had a very good experience with the car seats on planes. Granted, I usually fly with DH so that makes it easier. Alone is tough!
How many of your flights were international flights on not US carriers?