One year ago we booked our Alaskan land/cruise on the Sapphire Princes cruising 30 Aug, for a balcony room. About 5 months ago our TA called and said we could upgrade to a mini-suite for $100.00 per person, of course we jumped on that (along with two other couples going on the curise - one couple stayed with the balcony). The couple with the balcony kept their room assignment (which is a good room) and one of the mini-suite couples received their cabin number about 2 months ago. Us and our friends still do not have our cabin numbers, but show that we are guarenteed a mini-suite.
When I have talked to Princess lately they tell me that there is a good chance that we will be upgraded - the longer the wait the better the chances. I don't know how true that is, but I like to think it is true! I would do the guarentee again - our prices were great and now I have hope of an "even-better" mini-suite for the last part of our vacation.
Hope this helps.