mtjewell81 - Island-hopping on boats is done a lot and often there will be people at a popular dinghy
dock asking if you are heading in a certain direction and if you have room aboard for guest.
The problem for skippers is that when you clear into a country you have to enter all the persons aboard in your clearance papers, likewise when you leave. If there is a discrepancy then the boat (and skipper) might get held up and not allowed to leave, depending upon the country. Normally when you know that a crew member
is leaving by plane you will present the ticket when clearing in and the immigration official will enter it into the form so that you won't have problems departing. Likewise a signed document from a skipper
when flying in on a 1-way ticket is often used in lieu of a full ticket.
The French islands are pretty cool about crew changes (particularly if the boat/skipper/crewmember is from a Schengen country) but other places such as the BVI or Antigua
are much more difficult and sticklers for formalities and the USA is very difficult for non-US citizens or LPR's (landed permanent residents) as everyone aboard requires a visa when sailing into the USVI, PR or the continental USA.
I've turned down guest rides from one island to the next before because I just didn't wish to deal with the responsibility and paperwork hassles and other times when heading to St. Martin or Guadeloupe
I've taken guests aboard.