It looks like the Passport Card is ONLY good for entering / exiting the US from Canada, Mexico, the Caribbean, and Bermuda. It CANNOT be used for International travel by air, so most people don't think this is a good idea. In other words, if you go to Europe, or for that matter, Mexico by air, then you must have a passport book in order to enter / exit the US.
is the link to the information directly from the Unites States State Department.
2007 - Majesty of the Seas
2009 - Enchantment of the Seas
2010 - Freedom of the Seas