I tend to agree with Pea and the others - I think Carnival would be shooting themselves in the foot (or higher) if they messed around with Princess. Yes, some changes will probably take place. I've got 3 cruises booked with Princess in the next 10 months and I'll judge from that. That being said, if I could get similar prices and itineraries for where I want to go on one of the Celebrity Millenium class ships, I'd chose that over Princess.
For now though, I'm going to want to see if being a Platinum Circle Club member provides any other worthwhile benefits other than free internet, which BTW, is meaningful to me.