As others have said before, it depends. Most of all it probably depends on your personal feelings towards a song, but also what kind of song it is. I don't mind 'The Boxer' - a song I like, btw - being turned into 'The Folker', which I think is hilarious. Somehow I DO mind Eric Bogle's anti-war songs being parodied. They may have been done too much - No Man's Land, certainly - but it's still a first class song about a very very serious topic. In the same way, I might resent a parody of 'The Freedom Come-All-Ye' or something, but not of a traditional ballad (not most of them, anyway). Others may - and obviously do - feel very differently. It's down to personal taste and emotion.