I don't have Flight Sim X yet (I need to build a PC to run it properly first), but I do have the previous version, along with the USA Roads add-on.
I don't play it like most people though. I basically just stick to the learjet, and fly around the world, many times pushing the maximum range of the plane to it's limit. I keep written logs of departure and arrival times, distance traveled, airport, runway and landing pattern (as specified by ATC). I spend most of my time on auto-pilot though, only take control when taxiing to and from runways, and on takeoff and landings. I also use time compression, alot. I use flight plans, but primarily only use VFR (due to the time compression and the fact that I'm pushing the plane to it's maximum range, which requires fuel conservation, which is easier in VFR than IFR, IMO).
I enjoy the simulation, and like almost all of my other simulation games, it allows me to multi-task and do other things while playing.