I have 2006 X5 4.4. I had it for about 1 yr now with 15k. Previously I had 2001 MB ML320, for five years, several problems like broken window switch, ... etc. Nothing major, not a single time that car stoped.
On the other hand with X5. Yes it is a lot better acceleration & ride compared to ML. It should be for about $20k more. Three wks ago on Sunday morning after car wash, car never started again. X5 was towed to Riverside BMW, and I asked for Mr. John Horgan. I read about his good reviews here previously. No rental car of course, since I bought mine from Shelly BMW. They kept mine for two days, and they claimed that it was all fixed up. On the freeway back from Riverside BMW, engine failure warning kicked in and RPM hits floor. Every warning lights on the dash flash like crazy. I was on the first lane on interstate 15 N. Thank god traffic was light that day, otherwise I would have been stucked in middle of freeway. I called Riverside BMW, and explained what just happened. They towed X5 again, and guess what this time round, they had X5 as loaner ready. I guess they realized they did something wrong. This time it took them 3 days to figure out the problem, moisture in main computer chip, and 3 more days to fix everything.
After all, BMW service sucks compared to MB (MB service is not the best either). Yeah BMW covers breaks and 4 yr oil changes...etc. But when your car really needs service, all dealer service depts are all filled up for days. They wouldn't even look at your car for days. Service depts are already filled up, but BMW usa wants to bring in 1 series next year. I bet it is not going to get better than now.
By the way what is wrong with BMW loaner program. If we get toyota camry as loaner from enterprise, why did we pay extra $30-40k for BMW?? toyota camry owners get camrys as loaner from toyota dealership!!