A new crop of "sharing" services lets social-media users impart information about everything they're buying and everywhere they go. While the potentially rich cache of data can be a boon to marketers, the new spirit of sharing walks a fine line and often spills over into the too-much-information zone, say some. "People are not necessarily thinking about how long this information will stick around," said Chris Conley, a technology and civil liberties fellow at the American Civil Liberties Union.

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