Recently, investors celebrated the birthday of the current bull market, which turned five years old. On this anniversary, it's worth reflecting on how valuations, particularly of technology companies, are being calculated. On Thursday, the Wall Street Journal reported that Airbnb, a travel rental company, which has not released information about its revenue or profitability, may be approaching a valuation of $10 billion. Other startups in the IPO pipeline include a number of unprofitable companies like Box and Square, with rumored valuations in the billions. Have billion-dollar or multibillion-dollar valuations become the norm ? Is it all about hype and greed nowadays ? Whatever happened to the wisdom of investors like Warren Buffet who evaluated companies based on their profits and fundamental performances ? The value of any company is a function of the cash flow it will generate in the future. A healthy cash flow allows a company to repay its shareholders and initial investors who, understandably, expect their investment to be eventually reimbursed. Ordinary investors who rely on the hype surrounding a company rather than the company's fundamentals may make decisions that they regret later on. Just ask anyone who invested in the Pets.com IPO about the danger of falling for overvalued companies. Granted, everyone in the tech industry -- from startup founders to venture