PointsHound says that it gives more generous rewards to repeat users.

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If a search engine can provide consumers with the newest, freshest links from the social web in a way that makes sense, they will undoubtedly attract repeat users.

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The 33 million figure Pincus quoted may then have been the number of unique, rather than repeat, users.

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But on a cell phone with bad reception, users must often repeat themselves.

ECONOMIST: Internet