I have a 2011 X5 35D, and it just hit 50k miles.
Only 1 issue so far is was the alternator pulley going bad.
Other then that, car runs smooth and quiet. Never felt any of this vibration you guys are talking about. I switched from a E92...

For maintenance on Diesels, carbon build up is a bit more severe then Gas.
I would recommend more frequent oil changes then what BMW recommends.
Now that the truck is out of warranty, I started using Cetane booster. I plan on keeping this truck for a while.

You will love the 35D.