I'm attempting to teach myself Japanese (luckily I can go to class in September so I won't have to struggle any more on my own, yay!). I've been learning for a few months from a text book. I have learned quite a bit but I'm still not very good, lol. (In fact, I have a Japanese friend that I can talk with on the phone sometimes to help my pronunciation.) I think it's possible to learn quite well from books but obviously not the pronunciation; that's where 'learning by yourself' completely is no use.
It's satisfying to be able to listen to songs and pick out bits of what people are singing. I'm like a little child - "hey! I understood that!" Also, looking at the translations is interesting coz you can see how it has been changed to make more sense in English (or whatever) and compare English translation on the net with your own knowledge. I'd say music isn't so much use for learning, but it has got good use, in vocab, because often I'm listening or trying to translate and I'll find a word I don't know and make the effort to look for it and make sense of it. So, I've expanded my vocab, which now includes lots of really useless phrases, lol!
But, I guess songs are often distorted in a way to make them more poetic, in the same way we do with lyrics in English.
Oh, and incidentally I learned hiragana (not started katakana yet, but the hiragana were quite easy to learn so I imagine the katakana won't be too bad...) - that enables me to use the dictionary. Kanji looks to be way out of my league for a good long time...!