I am a certified car seat technician and we NEVER fly without a car seat for my daughter, even when she was under 2yo (she's 2.5 now). The issues regarding turbulence are VERY real and the comments about keeping your child happy and strapped in their seat for the duration of the trip are very true in my experience.
We've taken two trips by air to date and will be cruising in January w/ her and will be flying to FL. Each time she slept like a rock on the plane rides. This past October we flew to Orlando and on the trip home she was the ONLY child over 2 in a car seat and also the ONLY one to sleep the entire ride.
The Sit n Stroll is a decent option. It covers both stroller and car seat in one fell swoop...however like most things that do double duty it doesn't do either very well. It can be heavy and sometimes a bit too bulky to use in many instances.
Using your car seat from home is definitely a very good option. It's your seat, you know how to install it well and your child is used to it. We have a Britax seat which is on the large side and have a Samsonite Micromover luggage cart that has built in bungees and folds up small enough to put in dd's backpack diaper bag. We also have a lightweight stroller that is a breeze to use in the airport. It is a bit of a challenge to get everything through the line to check the luggage (for longer trips like a cruise) but once it's checked it's very easy. One of us takes the stroller w/ dd and the other pulls the carseat on the mover. We even put some carryons inside the seat.
I wanted to add this VERY good link to info about flying with a carseat....
Post Edited (12-29-03 15:38)