Haha, that might be the reason why I couldn't follow their words and the subtitles simultaneously. They simply didn't match.I am sorry my very first post is off-topic, but if the couple you mentioned in Lost are Sun and Jin Kwon, they are Koreans, not Japanese.
To come back to the original topic: Do you think the English sounds [f] and [v] are difficult for native Korean speakers? They shouldn't be, because the sound [φ] doesn't exist in Korean.By the way, I myself learned the IPA when I first learned English in middle school. Although I still have accents in my English pronunciation, learning the IPA (with all the crazy tongue pictures and vowel charts) helped a lot distinguishing different sounds. (Actually the system helped even more when I learned French in high school.)