I just traded my x5 for which I Had purchased the BMW extended warranty. They told me it is only transferable if I sold the car to another person. It is not transferable if the car went back through/to the BMW dealer through a trade and then resold on their lot.
My x5 was a 2007. It had 7 months and up to 40k of additional miles left on the warranty so I thought that would be a reason to get more for my trade as that would be peace of mind to the new buyer. And that's what they gave me.....so I cashed out the remainder of the warranty and am awaiting some $.