It's true Lori. They changed the rules for new bookings made after 1/1/09. Now you can only use one OBC from either the Next Cruise booking, Diamond discount, or stockholder benefit. You can't combine those. You can still combine credits you might get from your agent, or from the RCI VISA card, etc., with the above. For instance - on my next cruise I could only use my stockholder benefit and OBC I got from my Visa card points.
This change created a big uproar. They actually started it last fall but held off until the new year after the outrage.
The future booking (Next Cruise) has no expiration if I recall correctly.