6. LinkedIn

What it does: Social networking site for working professionals.
IPO Date: May 19, 2011
Money raised:$360 million

People began mumbling about bubbles when the eight-year-old "Facebook for professionals" announced it was going public. Despite pulling in $243 million revenue in 2010, LinkedIn said that it would be selling 7.84 million shares priced at $35 each, giving it a market value of $3 billion. On its IPO day, shares went for more than double the expected price at $86. To save its ass, LinkedIn cautioned that its growth is expected to slow in the future. Good one.