I had read recently that BMW is recommending NOT to rotate tires on their vehicles. Now don't ask me to back that up, because I'll have to spend 2 hours looking for the source...and I'll do it too!

The reasoning went something like, due to the different wear patterns on the front and rear tires over time (caused by different cambering), rotating can cause the tires to not grip as well by exposing unexpected wear patterns to the road surface when cornering.