Answer: $4 billion

The online file-sharing company received $250 million in venture capital at a $4 billion valuation, according to The Wall Street Journal, which reported that the company even secured celebrity investments from U2's Bono and his bandmate, The Edge. At that valuation, five-year-old Dropbox is worth as much as companies with multi-billions in revenue, such as Cablevision Systems Corp.and Expedia Inc.