Hmm, let’s see…

chan: is used for kids, girl friends (I mean female friends), and close family members mostly. For example: Yoko-chan, obaachan (granma), okaachan (“mommy”).

san: can be used anytime and you’re the safest using san. Carries a tad of respect and if you just met someone you should use san.

kun: is used for younger or lower social status people, as well as friends (guys). For example, my boss or my teacher call me Hao-kun.

sama: is even MORE respectful. I don’t ever say it but it is commonly used in emails directed to staff from the Embassy, my Japanese teacher, work contacts, etc.

And on the other side, if you don’t say anything at all, it means that either you’re friends with the person or your social status is higher. But when you’re talking about your own family, friends, or yourself, don’t use “san”.

To be on the safe side, use “san” always (even when you’re called other stuff, except when it’s an 8-year-old or when the person explicitly tells you not to call you san), and when talking about people in your circle or yourself don’t add anything.

Your question is quite interesting and I’ll be writing up a post about it this week =)

Off topic… whats the difference between san, kun, sama, and chan?

Sí, sería bueno pero vamos a ver =) es muy temprano para generar aún más expectativa! Los de computación tenemos suerte y talvez yo también pueda entrar a Todai (o al menos ganarme la beca!)

Esa carrera de informática creativa es bastante conocida por allá y talvez en el futuro si gano la beca pueda conocer a esa persona ^o^

Well, actually if you look at images from other posts like this one you’ll see that the watermark dances all over the place =) the default place is the bottom-left corner, but if it doesn’t look that all too well in there, I choose another place (I’m watermarking images by hand, but it doesn’t take too long, at least compared to the writeup and formatting)