LinkedIn won't be mistaken for Facebook anytime soon, but the professional social network crossed the 100 million member mark March 22 and is adding 1 million users per week.

LinkedIn launched in May 2003, which means it took almost eight years to hit the century mark in users. Contrast that with Facebook, which hit the 100 million member mark in August 2008, or four and a half years after it launched in February 2004. The leading social network now has more than 600 million users.

Facebook's counterpart for the workforce has expanded its offerings from helping users network and find jobs to helping recruiters groom new hires and entrepreneurs start new businesses.

While becoming a LinkedIn member is free, the company makes money from advertising, premium subscriptions and professional recruiting services.

Under CEO Jeff Weiner, LinkedIn filed for an initial public offering with the Securities and Exchange Commission in January. The company launched LinkedIn Today, which funnels relevant news users are sharing via LinkedIn and Twitter.

Now the company is celebrating the century mark, culling all sorts of factoids and stats about members and their profiles (anonymously, of course) via this infographic.

For example, LinkedIn calculated over 1.3 billion connections between members; 79+ million job transitions/changes tracked; and the fact that all of the Fortune 500 companies have executives on LinkedIn.

For more, read the eWEEK article: LinkedIn Cracks 100M User Mark Amid IPO.

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