One thing I find completely fascinating is musicians who drastically change their songs from demo version to final release. None of the bands I've been in have ever operated that way and I know plenty of other people in bands who don't operate that way. Actually, I only know one musician who it seems like almost always changes his songs from demo version to final version. I know that sometimes it's encouraged (or demanded, ha!) by the producer or engineer. An example of that is this song, Fairy Tales, by the Stockholm Monsters. Most people thought that the version Martin Hannett demanded out of them was not as good as their demo version. Of course, the funny thing is that it's a matter of personal taste, isn't it? I love the Hannett version much more than the demo.
Fairy Tales (Demo)