I just received an email from Carnival that there will be NO replacement port for Costa Maya. Instead they are providing a $25 per person credit to your onboard Sail & Sign charge account. This applies to all Glory Western Caribbean bookings made prior to October 8th 2007 for cruises of December 1, 2007 and December 29, 2007 to April 10, 2008. I looked on the Carnival site and it reflects the Itinerary change there as well.
So another sea day it is. I can live with that.