Was originally planned as a 30-45 minute in-flight movies for Japan Airlines. Director Hayao Miyazaki eventually expanded it into a feature-length production.
The song that Marco (Porco) is listening to on the radio in the beginning is "Sakuranbo no Minoru Koro", which is the song Gina will sing in a later scene.
In the pirates joint attack sequence you can read on the front part of one of the pirate planes: "Morte ai porcelli!!" ("Death to the pigs!!") (Even though the first R is spelled like a N, but it may just be the handwriting...)