This topic caught my eye.

I'm not Japanese, but I started studying Japanese
12 years ago, as a small child. Nothing is more
irritating to me than reading a fanfic or a post
and finding people spout off "mata ne!", "ja ne!",
"sou ka" etc. From my best guess, it seems like
people are trying to look cool by showing that
they "know" Japanese. A lot of the people who are
bothered by the use are bothered because they
don't understand, I am bothered because I do
understand and find that often the users use these
very informal phrases when they should be using
more formal phrases (do you say "check yo' later"
to your boss or someone you don't know?). Most
Japanese would be put off by the tossing around of
such casual phrases.

Also, it is obvious that the people running around
with handles such as "Miki-chan" are not Japanese.
A Japanese person would not refer to themself as
san, chan, sensei, sempai, etc. It's like calling
yourself "Mr. (your first name here)".