It just all depends on a lot of factors. I can tell you that I cruised last September and got an upgrade. I booked directly through Disney on July 4th weekend for a category 11 (because that was the lowest priced category at the time) and ended up getting upgraded to a category 8. I have heard your chances are better if you book a guarantee (just a particular category) instead of a specific cabin #, but I really don't think there is any rhyme or reason to who gets an upgrade, it's just luck. Good luck!