For those who are "learning" by listening to music, watching anime etc etc, I strongly suggest you take a some classes first, then do whatever you guys do to learn, it'll be alot easier that way, since you will know the do's and do nots. Because it would suck if you did in fact learn, but you talk like a girl, and you're a guy, or you talk like an informal prick, when your trying to be polite, and once it's become habit, it will be very hard to break. When I was in classes in Japan, one of my teachers gave me this site
japanese.about.com
It's one of the few sites that give you the basics, Kanji, Kana, do's and do nots, all forms of conjugation, particle use, etc etc I wish more sites, listed the do's and do not's.
There's this one guy in my Art class here @ USC, who swears he learned Japanese from Gundam, so I started talking in the little Japanese he knew, and well let's say he has ALOT of learning to do, and he makes alot of mistakes in use of conjugation. Then he talks about how he wants to move to Japan, because he read all these books, so he knows how it is living there.........god if only he knew