ananyo writes "When influenza hit early and hard in the United States this year, it quietly claimed an unacknowledged victim: one of the cutting-edge techniques being used to monitor the outbreak. A comparison with traditional surveillance data showed that Google Flu Trends, which estimates prevalence from flu-related Internet searches, had drastically overestimated peak flu levels. The glitch is no more than a temporary setback for a promising strategy, experts say, and Google is sure to refine its algorithms. But with flu-tracking techniques based on mining of web data and on social media taking off, Nature looks at how these potentially cheaper, faster methods measure up against traditional epidemiological surveillance networks." Crowdsourcing is often useful, but it seems to have limits.