We did this on our Hawaii cruise. We were told we would get our cabin assignment when we got our docs. When the docs arrived where the cabin # should be it just had TBA. Called our agent and she had never had this happen before. She checked less than a week before we left, and still no assigned cabin number, which made me a bit nervous. When we arrived we were thrilled to find that we had been given a fantastic extended balcony that we used quite extensively on our trip. We haven't booked a guarantee cabin since then because we have taken our kids on our cruises and needed to make sure our cabins were together. I wouldn't hesitate to in the future, though!