I think this question on Rooibos tea inspired the current question.

Original post from Stephan of Whole Health Source touching on polyphenols similar to Acton's quote.

Conventional wisdom claims that there is strong evidence that fruit and vegetables are great for health and by association polyphenols. Don at Primal Wisdom does a good job showing how weak this evidence is.

Nephropal shows some of the evidence supporting anti-oxidants.