But Uber's own investors say the company is just getting started. Bill Maris, managing partner at Google Ventures, has estimated the valuation could eventually hit $200 billion. One way Uber is looking to boost revenue is through an ambitious expansion in emerging markets.  Last week, chief executive Travis Kalanick said he would double down in China, aiming to reach 100 cities across the country over the next year. He touted the company's growing market-share in the high-growth market, which he says stands near 30 percent, up from a 1 percent just nine months ago.  But that's a small piece of the pie compared to domestic rival Didi Kuaidi, which still claims to have 80 percent market share. Didi Kuaidi confirmed last week that it closed a fresh $3 billion fundraising, just a day after Uber announced its own $1.2 billion raise in a China-focused round. Didi, and Uber's Indian rival, Ola, have also proved willing to go to great lengths to preserve market dominance through a virtual price war.  The determination of Uber's rivals around the world has led some tech investors to doubt the merits of Kalanick's growth strategy.  "The question is how much they have to invest in each new city to get it to profitability, given the amount of driver and passenger discounts and incentives they provide to get going. I think emerging markets will be tough," Rob Moffat, a principal at Balderton Capital told CNBC.  Still, the private equity arm of Indian Conglomerate Tata announced last month an investment in the Silicon Valley group, estimated to be worth $100 million. The managing partner of the fund, Padmanabh Sinha, explained on CNBC's Capital Connection that he was impressed by the initiative Uber took by reaching out to an Indian-focused investor. "It shows the nature of the symbiotic relationship," Sinha said.  As Uber moves full speed ahead trying to tackle the emerging market behemoths, the company is also seeking new revenue channels in the U.S. The group is reportedly set to announce new delivery partnerships with dozens of retailers and has been busy launching its UberEats service in new cities.  Nevertheless, Hawtin warns potential investors not to discount the evolving competitive landscape for private tech firms. Drawing parallels to Spotify's $526 million fundraising, which closed within weeks of Apple's music-streaming announcement, he warned investors not to be blindsided by the "risks involved in a company that is not readily tradable."  Even if investors are willing to stomach the competitive risks, the fickle regulatory landscape could keep the bulls at bay. Uber has survived numerous taxi protests in cities around the world, and won a major concession from New York City officials in July who scrapped plans for a vote that could have limited the group's expansion.  But more recently, a US judge in California said that a lawsuit brought by drivers against Uber could proceed as a class-action case, potentially re-classifying drivers as employees, not contract workers.  Uber intends to appeal the decision but if that distinction is eventually forced on the business, it could significantly increase costs and pose the biggest threat to Uber's $50 billion price tag yet.  Follow us on Twitter: @CNBCWorld
For a six-year-old firm that has never turned a profit, the $50 billion dollar question remains: Do the numbers add up?