We met a couple that was doing their 100th. cruise with Celebrity and they had 40 other cruises on different lines.
They never got off the ship anymore because they had been to all the ports several times.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Independence of the Seas 12/29/2013 Top-notch!