If there was any doubt in your mind...

... that we are in another bubble, this should dispel it. Groupon, a three-year-old company with zero profit, is filing for an IPO. Why do they need the money? Because they took all of their previous investment rounds and paid them out to earlier investors:

In January, Groupon raised $950 million. By the end of March, it had $209 million in cash. What happened to all that money? The company’s IPO filing spells that out: Almost all of it went right back out the door, to employees and early investors. ... Of note: This wasn’t the first time Groupon had raised money and taken cash off the table. In April 2010, the company raised $130 million, and handed $120 million to many of the same people.

If it quacks like a Ponzi scheme...