We got ours stamped coming off the ship on our last cruise, but didn't think to do it at any of the ports!! Someone told me you can go to the post office in most ports, but we forgot - even though we actually WENT to the post office in Nassau to buy stamps...
Carnival Elation March 11
Carnival Imagination Sept 07
Carniival Sensation Dec 06
RCI Sovereign of the Seas Sept 06
Carnival Miracle Sept 05
Carnival Glory Sept 04
Carnival Fantasy Jan 04
In our experience very few Caribbean islands bother to stamp your passport if you're there on a cruise. Some of them do if you fly in. I think it's interesting that the most INCONSISTENT nation in this regard is (the envelope please), the United States of America. Sometimes they do, and sometimes they don't, whether you're cruising or flying. You just never know. This has always been the case, but I had thought things would tighten up after 9/11, with all the emphasis on "consistency."
I've never tried to get a stamp anyplace that didn't do it without my asking. Frankly, searching out a passport stamp seems to be not the best use of your time in port, but to each his own.
Some people like to get stamps to show where theyve been. My first passport is loaded with them from studying in Europe, although I never got stamps while on a train. I wish I had known about getting them in port. I wouldve made an effort to get my sons passport stamped. I do keep a travel journal about where hes been though, but the stamps would be neat.
When the immigration official at a port of entry stamps your passport, he or she is actually giving you an "on the spot" visa, or in other words, permission to enter. That permission is memorialized by the stamp. In many countries with tighter controls, they also stamp you out to show that you've left. Some visa stamps specify the conditions under which you are admitted (such as length of stay, the fact that you're not allowed to seek employment, or whatever). And the stamps always carry the date. Ultimately, if some official of the country you're visiting looks at your passport, it's easy to tell whether or not you've entered legally.
But, often as not, some countries--especially little Caribbean countries--just don't bother stamping cruise passengers' passports. Part of the reason, I guess, is that they don't really feel they have either immigration or terrorism problems, so why waste the manpower.
Just for the record, there are some countries that require you to have visa stamps placed in your passport BEFORE you arrive. That's why it's always wise to check visa requirements before you leave on an international trip, even though you have a passport.