Facebook's 'like' icon at its HQ in California
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Just how valuable is Facebook?

The world's largest social networking site, Facebook, is to have its stock market launch with a value as high as $100bn being estimated.

The company, founded by Mark Zuckerberg, wants to raise around $5bn.

If attained, it would make it the biggest first-time share sale for a technology company.

Caroline Hepker reports.