I can't make my mind up about the Mumfords - part of me is pleased to see a talented bunch of musicians who can actually play suddenly becoming popular, and they are clearly a great live band, but the 'folkie' part of me can't really get into the stuff they play.
I suppose if a tiny fraction of their fans decide to look a bit deeper into their background and investigate artists like Show of Hands, Bellowhead, Fairport Convention or Oysterband or any traditional musicians, it has to be a good thing.