I purchased it exactly 15 months ago as a cpo with the 6yr/100k warranty but hardly ever needed it during the 30k i put on it. very few things have gone wrong like a minor rattle from the engine bay turning out to be a/c fan plastic clips and failed driver side window switch after i left it open in rain by mistake (my fault). dealer fixed both, no questions asked. other than that, its been excellent & trouble free and i've taken it on numerous long trips since i owned it. the interior comfort and materials fit & finish is top notch and exterior looks good too. I've the 3.0i which has excellent low end torque (take off) but OK highway torque (you need to step up to the bigger v8s for better)
i've the factory base model, no options other than auto transmission. i really didn't care for options as i need reliability more than anything else (i drove a 07 toyota prius before this and couldn't stand it anymore (boring)- but then it was 100% reliable for the 2yr/60k miles i owned it - i never ever took it to a dealer for anything other than oil changes) and i'm very happy to say that this cpo'd x5 has been super reliable too. I avoided the bigger v8s since i used to have a few bmw 7-ser v8s (2005/2008/2003) and there was always something wrong with the engines in them. Also, if you plan to get any bmw cpo, check the service records & certification report just to make sure they add up
lol, nothing can be improved now since its last year was '06 but i wish it had more trunk space and oh, the stock stereo/speakers sound like crap. maybe germans don't care about listening to music on the way to work but we do. i'll try getting the speakers changed sometime.