Marginal Revolution University: Does Fair Trade Help?
Economist Tyler Cowen gives his take on the impact of Fair Trade coffee. For a more detailed analysis I'd suggest Victor Claar's Fair Trade? Its Prospects as a Poverty Solution.
I know many activists are passionate about Fair Trade coffee but I don't see their certainty about the benefits reflected by economists who study the practice. I suspect that same could be said for most commodities. (It may different with non-commodity efforts like hand-crafted goods.) But generally speaking I think the advice to buy coffee at the best price and give the excess you would have paid for Fair Trade coffee to a good charity is good advice.