[godwine]

I could be wrong, so do wait for MMM or Nagoyankee's reply, but according to my uncle (local Japanese), a lot of reponses used in J-Drama and animate are consider slang and bad/impolite form:

I understand - Proper form would be "Wakarimashita", short slang form "Wakada"

Amazing - Proper form "Sugoi", short slang form - suge

Things like that, I don't know the full list as I don't know them for the most part, and if I do use them my uncle get upset at me, so I pretty much just sticked to whats in the book.

Again, I could be wrong, given that uncle is one of those extremely old fashioned Japanese that won't even let my girlfriend sleep in the same room with me when we visited Japan