In The New Marketing Manifesto, John Grant noted 'Authenticity is the benchmark against which all brands are now judged'.
Also - in a moment of arch-ness - Seth Godin said in Permission Marketing: 'If you can fake authenticity, the rest will take care of itself.'
I'll take the word from the bird...
UPDATE: Some younger readers have expressed confusion over the 'bird' reference.
Charlie Parker was known as 'Bird', short for 'Yardbird'.
Yardbird is a jazzbo colloquialism for 'chicken', a young Parker is said to have hit a chicken with his car by accident while on tour with the Jay McShann Orchestra, and proceeded to cook and eat the unfortunate fowl later that evening post gig. Fact fans.