From Hal Varian's column
in today's NY Times:
The professors look at how a company’s stock responds to a cover story in BusinessWeek, Fortune and Forbes. They find that positive stories follow periods of positive performance and negative stories follow periods of negative performance, which admittedly is not too surprising. More interesting, they also find that the appearance of a cover story tends to signal the end of the abnormal performance.
My advice for most investors: Put your trust in tax-efficient index funds