Run that by me one more time.  A California start-up whose only product is an app that gets you to reserve the most expensive "taxis" on the road has raised $18 billion? Really?

In raising that heretofore unheard of capital, Uber Technologies, Inc. has become the most heavily funded venture start-up in the country.

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It's just raised $1.2 billion in a new financing led by Fidelity Investments to bring its valuation to about $17 or $18 billion compared to $3.5 billion in financing last year.

Other investors in the new round were heavy hitters Summit Partners (one of the 50 largest private equity firms in the world), Wellington Management Company (in the same league as Summit), BlackRock, Inc. (the world's largest asset manager), Kleiner Perkins Caufield & Byers, and existing investors such as Google Ventures and Menlo Ventures.

Uber CEO Travis Kalanick said he was keeping the round open to strategic partners that might part with an additional $200 million.

Including Uber, there are only some 30 companies belonging to the billion dollar venture capital club so far. Uber's success in raising tons of cash can be better appreciated if one realizes that among the other members of this elite circle are guys like Pinterest, which raised only $5 billion, and Dropbox, which took in $10 billion in venture capital.

To put it in another way, Uber is now worth more than half of the firms in the Standard & Poor's 500-stock index that includes a horde of established tech companies, banks and oil companies.

So why is a mere ridesharing app the hottest thing on the street? That's precisely what's worrying a growing number of financial analysts who keep seeing the phrase "tech bubble" inflating in front of their eyes.

Uber's über success in raising venture capital is resurrecting talk of a particular piece of painfully earned wisdom from the Great Depression of 1929.

The late businessman and millionaire Joseph Kennedy was reputed to have said that "When even shoeshine boys are giving you stock tips, it's time to sell," meaning that everybody's jumping into the market for the wrong reasons. It's not this bad, at least not yet, according to some analysts.

"This is about capitalizing for the opportunities that we see ahead of ourselves," said Kalanick. "If you can make it economical for people to get out of their cars or sell their cars, and turn transportation into a service, it´s a pretty big deal."   

Based in San Francisco, Uber makes an app that connects passengers with drivers of vehicles for hire and ridesharing services. It arranges pickups in dozens of cities around the world.

TagsUber, App, taxi