The plane that Quinn flies is a DeHavilland Beaver. Star Harrison Ford not only owned a DeHaviland Beaver, but he also flew the one in the movie. He had to go through several certifications for the insurance company to allow him not only to fly, but to also fly with the rest of the cast in the plane.
Temuera Morrison and Cliff Curtis are speaking Maori in their roles as pirates. However they didn't know how to say the complex lines they were supposed to (about gold and pirates, etc), so they just ad-libbed random everyday stuff such as what they were cooking for dinner. (From Temuera's biography "Temuera Morrison: From Haka to Hollywood").
When Robin (Anne Heche) asks Quinn (Harrison Ford) what age he is, Quinn hints that he's over fifty before whispering to her the answer (To which she says "You still look good," and Quinn replies, "I still am good!"). Ford was actually 55 by the time this movie came out.
Jacqueline Obradors' parents are from Argentina. Her character is supposedly a native Pacific islander. in the film she hurries up her boyfriend saying "dale metele, pibe", which is an Argentine slang phrase meaning, more or less: "c'mon, boy".