I do not rotate the tires on either my '99 328 or '96 Z3. The tires on the Z3 wear evenly (across the tire), but the rear tires only last half as long as the front.
On the 328, the rear wore very unevenly. The inside edge, near the inside sidwall, wore a deep groove. I could not see it unless I looked very closely from the rear. I found out how deep it was when I heard a hissing sound and investigated. Lucky I didn't have a blowout at speed. Learned a valuable lesson, check the entire tire carefully and regularly. I asked service writer at the dealer and the first thing she asked was, "Wow often did you rotate them?" I told her that my owners manual recommended not rotating, she simply walked away (I don't like her very much, I think the feeling is mutual).