Even though it hasn't announced plans to go public, the taxi-disrupting car hailing service Uber has already made a handful of early investors uber-rich.

According to a report in Fortune, Uber's current estimated valuation of $17 billion means that angel investors have made as much as 2,000 times their original investment in the four-year-old company. A $20,000 investment in the angel round would now be worth around $40 million dollars, the story says.

But that's not to say that Uber doesn't face enormous challenges going forward. CEO Travis Kalanick is something of a polarizing figure, inspiring both admiration and emnity in the tech world.