A study published in January 2006 in Journal of Marketing: "It is possible to beat the market consistently by investing in forms that do well on the ACSI [American Customer Satisfaction Index." Consumerist, which has a pdf copy of the article, explains, "Companies at the top 20% of the the American Customer Satisfaction Index greatly outperformed the the stock market, generating a 40% return."
Interesting. Would it be possible to beat the ASCI's quarterly schedule by ordering your own Net Promoter surveys for selected companies? Is anyone doing this already? Comments? (moderated).
Update: here's a study from London School of Economics that links Net Promoter Score and company (and stock) performance.