"Most of what people print now is for temporary read-and-discard purposes and for transactions, " said Shane.

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The SEC requires private companies with at least 500 investors to disclose its finances, something companies like Facebook have vehemently resisted. (Read Facebook And Twitter Lead To Explosion In Private Company Stock Transactions).

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Working with big firms, Castlight assembles data from past transactions so that employees can shop for doctors online and read reviews posted by patients.

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