In general I don't like it when pop performers do traditional or folk. What I really don't like is when classically trained people do traditional - I find that usually they are focusing much more on technique than the emotion and the story. It's just a different style of singing, I guess. For me, traditional singing is about the song, and not the performer. You aren't showing off your voice, you aren't showing off your technique - you are the vehicle for the melody and the story. Having said that, I haven't heard it but I was told that Sinead did a very lovely version of "The Foggy Dew".