Downloading music - good or bad?

Tweet

Please note this is about music only - things get a little complicated when you extend the discussion to media in general, so please see my other discussions for Movies and TV shows. So yeah... What do you think about downloading movies? I don't think many people will claim that downloading a single song from a best-selling album is a heinous crime, but at the same time, many [including the law] would say that breaking into an artist's house to steal an unreleased single is criminal. So where does casual music downloading fit in? Where do you draw the line between fair use and criminal activity? Or is there no line?