I was interested to ready this article on the BBC Website Arts and Culture section
http://www.bbc.co.uk/arts/0/24810371It is apparently 100 years since the release of Danny Boy. I'm not sure about the fairies involvement in the original Londonderry Air (O'Cahan's Lament)

I love this haunting melody and find the lyrics extremely moving. I was surprised to read that it was in fact an Englishman who put words to the music (Frederic Edward Weatherly KC) who also wrote the lyrics for the wartime song "Roses of Picardy". According to Wikipedia he was a very musical Barrister.