Hi Kim! Welcome to cruise chat!
You can check with your airline to make sure, but last I heard, they were still doing this (at least for AA and Alaskan Air) You can find it on the AA website. It is definitely worth it if you plan on renting a car and exploring on your way to Anchorage. If you are taking the ships transfer, it might not be.
Carnival Cruise Lines:
Fantasy 90, Celebration 95, Victory 05, Conquest 05, Spirit 6/06, Freedom 6/08, Holiday 7/08, Victory 6/09, Valor 9/09, Dream 6/10, Splendor 8/10,Conquest 8/11,Magic 11/11,Triumph 4/12,Spirit 7/12,Freedom 11/12, Triumph 2/13 - The fire cruise, Magic 1/14, Freedom x 2 6/14
NCL Dream October 2006, RCCL Mariner OTS June 2007, Celebrity Silhouette 2013