An article by Michael Warburton, published as an Internet post on barefoot theory, seemed to spark some of the resurgence of the method of running. In his brilliant 2001 piece he had some interesting thoughts and pointed out some noteworthy facts. He indicated that research showed that an extra mass of 100 grams attached to the foot diminished the economy of running by one percent. Thus, two 10-ounce shoes (the weight of a lightweight training shoe) could have a compounding crippling effect on efficiency by more than five percent. In tangible terms, that could be more than six additional minutes for a world-class marathoner, taking a world record to a mere first-group finish.
link to Warburton article: http://www.sportsci.org/jour/0103/mw.htm