My 2010 built (MY2011) X6 has only had a problem with the paint - incorrectly repaired by the UK Delivery Centre at new and has needed a security update to help minimise thefts.
Other than a single instance of the dash failing to boot up properly (cause still unknown) it's been absolutely fine.
My E53 on the other hand was an expensive and fault prone embarrassment and was always in the shop.