We went back in May and the MB's shipped very quickly after the 30 day point. This time, the experience was different. I called around 11/4 (trip is 11/26). The first time the cast member didn't even look up my reservation. She just said "don't worry until you're ten days out." I asked what happens if they don't arrive before we leave and she said we would get gray bands at arrival.
The more that stewed in my head, I wasn't ok with that answer. I called back, spoke to a cast member who was happy to help, and got a better answer. He said they have been having an issue with nicknames (i.e., your name is William but your Magic Band personalization is Bill). We had a personalization, but he said he would call the distribution center and have them sent. We had MB's within a week! By the way - we used a nickname in May too, so I guess it is a "new" problem.