Firstly, apologies for yet another OT breakout, but this small 
cultural nuance can be very important - 

The term "otaku" has a sort of colorful history, and depending 
on where you use it and with whom, will come off either as the 
usual "I'm a fan" thing or as a major INSULT. Be careful.

I know that Japanese fans visit this forum, so I am curious 
what you guys have to say about this term in Japan.

    This is from the rec.arts.manga FAQ:

otaku ^[$@%*%?%/^[(B
     "Fanatic". Slang word for hard-core fans of anything, roughly equating to
     "geek", "nerd", "fanboy", or "freak". Thus, a manga otaku is someone whose
     life revolves around manga to an extreme degree. (In Japan, this would
     probably entail reading or buying well in excess of 2000 pages/week;
     outside Japan, probably about half that.) The word usually has neutral
     connotations within fan culture, but in other contexts, it can carry very
     negative connotations. In Japanese, the word "mania" means much the same
     as "otaku", but has less extreme connotations.

     Literally, "o-taku" ^[$@$*$?$/^[(J is formal speech for "your house",
     which is also a polite, somewhat distant, second-person way of saying
     "you". The word came to be applied to those fans or hobbyists who rarely
     got out and mingled with the rest of society.

     (It is interesting to note that the English "fanatic" derives from the
     Latin "fanum", or temple/house - "fanaticus" being a devoted worshipper.)

     It has been speculated that the slang usage of "otaku" was coined by
     Shinda Mane ^[$@?7ED??;R^[(B, a manga artist active in the early '80s. The
     term was popularised by freelance writer Nakamori Akio in an article for
     the June 1983 issue of Manga Burikko. The otaku entered public
     consciousness in 1989 with the arrest of serial killer Miyazaki Tsutomu, a
     dedicated anime/manga otaku.


From my experience - Western fans don't usually care if the 
term "otaku" is applied to them. Japanese fans are a whole 
other thing, depending on how much weight they put on the 
associated connotation from above (insane? serial killer? >_<).
But I've known some Japanese fans who didn't really care either, 
but perhaps they're the weird ones.