I also went back to FS9 (FS2004). FSX is the worst release since FS2000 imo (which was a real lemon). I guess the lack of competition has made MS get lazy. Maybe SP1 willk fix things but I'm not holding my breath. Hell, even with my new rig FSX still shows how badly optimised it is in built up areas with lots of traffic etc...
FS9 is their best effort of the franchise and with choice add-ons it looks lovely even 3 yrs later. You don't need to fork out a load of dosh either, go to Avsim or Flightsim and there is some amazing freeware stuff for it