I emailed the Ocean Players Club (to enquire how many points I'd accumulated) before our B2B2B cruises on the Fascination this past May. Dena responded and told me to go to the cashier's cage to pick up $50 credit (they handed over cash). I also received another $75 credit on the 3rd cruise, plus we each got a tote bag of logo stuff and the casino host bought our drinks 2 nights. In the past we've received the Bon Voyage decorations in the cabin plus the fruit and cheese basket.
I emailed OPC after we got back from the cruises and told them I'd be on the Miracle in Sept....Dena told me I'd have a $100 credit.
So, guess you have to put LOTS of money in the slot machines
Note that emailing the casino host is a different thing than getting casino credits, etc from Ocean Players Club