I view these types of threads with a chuckle. While you are all fired up about what you see as a completely flawed product, I am using FSX w/ Acceleration with 100% stability. The only problem I ever had with FSX was slow frame rates in dense metro areas. My system (P4 3.6 Extreme, 3GB RAM, Nvidia 6800GT 256MB, XP) is largely responsible for that. Sure, when FSX was released the engine required a large amount of optimization but since SP2, large metro areas are still a bit slow (10-15 fps) they are no longer down in the single digits with all sliders still set the same as the day I installed FSX.
I have installed several add-ons (Countless Eaglesoft aircraft, Flight Deck 4) and I don't have problems with those either. Even after I installed Acceleration, everything continues work flawlessly. Several others I know with "non-standard" setups (three monitors, non-standard controllers from FlightLink, etc) aren't having problems either.
So, if there are users out there with no problems to speak of, doesn't it stand to reason that the majority of the complainers need look no further than their own systems? Do you really believe that a software product can be 100% compatible with every hardware/software combination in existance? To expect such is completely unrealistic and unreasonable.
Moral? Before you go spouting that a product is flawed, take a good look around. If there are others who are having absolutely no problems with FSX, there is a better than average chance that your system and/or troubleshooting skills are to blame.