I'm cruising in August (on the Sun). We booked two rooms - one was a guarantee BC and the other was not guarantee (can't remember the class). The BC was upgraded to a BB. It's my first cruise, so I'm not sure what the difference is, but from the map of the ship it looks like we're on a higher deck (we're on Aloha). Since this is my first cruise, I can tell you that little bump in category was not due to any favored customer status. There was no category change for the non-guarantee room.
We have done guarantees many times on Princess (and other cruise lines). We usually end up with a better room than what we paid for. But the last few times on Princess
all we have gotten upgraded to is the highest caregory inside room. We were
just on Caribbean P two weeks ago. We booked a K guarantee and ended
up with an II on Lido deck. But the ship was full so there really wasn't
much chance of getting upgraded any more than that.
there is no firm and fast rule when it comes to guarantees. Your chances are better for an upgrade if you book a guarantee as opposed to booking a specific cabin. IF you choose to book a guarantee do not book a lower cabin catagory than what you really want in hopes of being upgraded, you could be dissapointed. Most of the time the upgrades are to a better cabin location in the same cabin catagory.