Well for me it's definately generally accepted. I love good music and I'm clever enough to understand that I'm not talented enough to create some really good worth attention music.
When it comes to my filming, music inspires me to make movies. If I am listening to some awesome horror music, I can easily start creating a horror movie and I can easily imagine the montage which is needed, the way I want to, the whole basic scenes, characters and so on. So after I film the whole thing and finish montaging, I add the music which inspired me to film that stuff. And most commonly it happens that the music I was inspired by is copyrighted.

P.S. If the movie is not for profit, there's nothing wrong about it. I mean it's art we guys are creating and it mustn't be stopped. It's not like we make profit from stuff which is not ours, and if we do, that's really serious and that's very bad.