A flood of money from unconventional sources has sent valuations of late-stage technology start-ups, including Uber and Snapchat, to levels not seen since before the dot-com crash. Hedge funds and mutual funds that once shunned venture-style deals are flocking to the market's hottest corner, paying 15 to 18 times projected sales for the year ahead in recent private-funding rounds.That compares with 10 to 12 times five years ago for the priciest companies.The torrid action is spurring talk that 15 years after the collapse of the internet bubble, the market may be setting itself up for another bruising fall."Some of the valuations are mind-boggling," said Sven Weber, investment manager of the Shares-Post 100 Fund, which backs late-stage tech start-ups.Companies now valued at 16 times future revenue could easily lose a third of their value in a market pullback that Weber say may occur in the next three years.Investors' appetites have been stoked by jackpots won in initial public offerings. Among the biggest: an almost fourfold $3.2-billion paper profit earned by Silver Lake Management in Chinese e-commerce giant Alibaba's record-breaking $21.8-billion September IPO. It was a quick kill for Silver Lake, coming three years after the private-equity firm's investment in the company.Snapchat is valued at $15-billion, based on a planned investment by Alibaba. Uber's valuation is up 10-fold since 2013, to $40-billion in December. ..