"Remix culture" is really nothing new. A lot of traditional music worked this way: Someone would hear several melodies, then they'd use fragments of them to make a new one. Someone would take a melody from one song and write their own set of lyrics.
"Remix culture" is just how things have always worked. It's just that now, we have all this digital technology to leverage for it.
This has been on Hulu for a while now, it's a great film to educate yourself on copyright law, particularly if you're a Girl Talk fan.