Got an 07 X3si sport too and we love it. We've only had it for 3yrs so far. It was the only SUV that we drove that handles like a car. So far the only thing that went wrong was the driver side seat warmer got too hot and melted a tiny bit of the leather, even though that particular part was not under the CPO warranty, BMW still replaced the seat as a goodwill warranty claim. So overall, we are very happy with our X3, no problems so far, but its only a 6yr old car (fingers crossed!).
2000 BMW 328Ci w/ Premium Sports Pkg, Type 68 OEM M-rims (summer), Type 67 replica M-rims (winter)
HK Premium Sound, Dension IceLink Plus (Stealth), Predator Chromiums 6000K, Tint & OEM Clears :}: