I had my trailer hitch installed by a local dealer, I got it as part of my original deal when I purchased the car. I believe the hitch installed was around $400.00 but they had given me a credit when I bought the car. They didn't install the wiring harness though so I still need to get back up there to get that done. Overall, I love the hitch. I only use it with a Thule bike rack to carry my mountain bikes, it works great. The installation itself though isn't a perfect one, I expect more from BMW. They do not offer any type of finishing cover to make it look like it is actually part of the car. I am hoping something is offered aftermarket. I also carry a cargo carrier on top, with the BMW crossbars, it looks pretty sweet and increases cargo load dramtically.
Let me know if you get the hitch installed. I would love to see a picture of the finished product so I can compare with mine.