LinkedIn reached 300 million members according to a story in USA Today.
The company was founded in December 2002 and launched on May 5, 2003, the company is now a publicly traded company and is currently trading at $175 a share, this equates to a market cap of $21.6 billion.
From the USA Today article:
Professional social network LinkedIn announced that the service topped 300 million members, 100 million of which are based in the U.S.
In a statement released Friday, Deep Nishar, the senior vice president of products and user experience at LinkedIn, says more than half of its global traffic will generate from mobile devices by the end of the year.