More than likely would end up buying the vehicle out ($399 lease end purchase fee), hard to find a four year old BMW for $18,000, could probably sell it and make a few of my lease bucks back at that point, what do you think?
Keep in mind two things:
1. History predicts that not long after the F30 goes on sale, E90 values are going to drop faster.
2. BMW sold many, many 2005 325i Executive Package sedans just before the E90 went on sale. When these were coming off lease in '08-'09, they were EVERYWHERE and could be had for very cheap. Same thing is going to happen with the '11 328i xDrive, IMO.