I had the 2011 x5 diesel built to my specs and delivered in Sept 2010. I loaded it up with almost all accessories which, like all German cars, add considerably to the price of the car. I now have about 26,000 miles on it. The car drives as close to a BMW feel as is possible for an SUV and continues to improve as the computer learns how you drive it. I am tall (6'3") and it is one of the few cars that truly fits me. We drive the car regularly between Seattle and the San Francisco Bay area, and it is hard to imagine a better car for this use.
I suspect that a low mileage used X5 would be the way to go for most folks. We bit the bullit in 2010 and ordered ours with all of the options. At the time, there was a hefty rebate on the diesel and a tax incentive of $5k . My wife and I both drive it and it has 66,000 miles. Brakes, tires and a battery is all we have done to it. Regular dealer and good independent service have kept the cost down. You don't buy one of these to save money. You buy it for the driving experience, comfort and safety that the Beemer is famous for. We get about 30 mpg on the highway and 24 in town. I had the dealer install the BMW trailer hitch package and it is worth it. I'll pull a horse or big utility trailer with it easily. The hitch is rated at 6500 lbs, but the same car in europe is rated at 7700 lbs. The hitch kit from the dealer includes an integrated trailer brake system hooked into the computer. They re-program the computer to "know" the trailer and lights etc. The shift patterns change when a trailer is hooked up. Pretty good stuff. BMW says the transmission and some other fluids are for life. My mechanic says to change them out at about 80K. I tend to believe him as it makes sense that any fluid will break down over time. Would I buy one again? Absolutely. New? Probably not. Probably get another diesel with under 10K miles on it. They are around and priced well. UPDATE 7/15/2017 The repair costs make the car a poor value if you plan on keeping it. We are having lots of problems with the diesel emissions system that are running into several thousand dollars. BMW has sort of addressed the issue but not entirely, The have issued an "Extended warranty" on some components but the car is constantly in the shop. I suspect the gas version may be better. Stay away from the diesel or buy the extended warranty and sell it before the warranty expires.
I have about 21,000 miles on the odometer and am mostly very pleased with the vehicle. Fuel mileage is frankly amazing for a 5200 lb SUV. Worst tank was 22mpg and best was nearly 28, overall average of 25mpg. It's fast enough for nearly any situation. It's a fantastic long-distance vehicle with a range of nearly 600 miles between fill ups, and grown-up back seat passengers have commented the rear is plenty comfortable. It also handles better than any other SUV I've driven. Complaints include some cheap plastic in certain places in the interior, an "upgraded" audio system that's just so so, some turbo lag off idle, turning radius is terrible, and you have to get used to the diesel noise.
Just took delivery of my 7th X5 after trading a 2009 35d for a 2011 35d. I loved the 2009 diesel, but road, exhaust, and engine noise were a little too intrusive. BMW refined the 2011 to reduce the "bad" noises while keeping "good" noise like the sporty grumble during acceleration. The suspension also seems to have been improved. It's subtle and the X5 is certainly not Lexus quiet, but I immediately noticed the difference: a more refined luxury feel. Press releases talk about new styling and engines, but not the improved suspension and noise reduction. That's a shame because those improvements address the only significant flaw in my previous X5. Good job BMW, you were listening.
This is an early review as have not even made it through the break-in period. The car handles like a dream. I did not get the sports package. The car is capable of taking corners faster than I feel comfortable taking them. The Diesel knock is noticeable during initial acceleration but once up to speed you really have to listen for it. The noisiest part of cruising is the tire wine. I-drive is a breeze to use.