I had frequent freezes and FSX crashes.
After updating UIautomationcore.dll and RadeonPro (www.radeonpro.info) FSX is stable like a tank.
Briefly about my rig:
I have FSX Deluxe + Acceleration (DX10 preview) on Win 7 64 Ultimate, Asus Crosshair V, AMD 1100TBE @ 4GHz, 16 GB RAM, Asus HD 6970 with 4 screens, cockpit hardware (Yoke, rudder, joystick, etc) + tons of addons (commercial and freeware). I did some well known tweeks in fsx.cfg and shader fixer (the freeware one found at AVSIM) to squize max performance of my rather not FSX friendly hardware.
I have installed: PMDG 737NGX, 777-200LR,F, 747, J4100, Majestic Q-400, ConcordeX, PassengersX, REX, GEX, ORBX GLOBAL+Vectors, FSUIPC, and more.