There's a big difference between the dot-com IPOs of the late 90s and the IPOs of today: revenues. Some may express surprise that Candy Crush generated $1 billion of revenue, or that Facebook generates $8 billion / yr; and some may not agree with the multiples assigned to these companies by the markets; but neither of those thoughts makes the current environment comparable to 1999, when pre-revenue companies with unworkable business plans IPO'ed at high valuations. What I don't see in this article is any analysis of the growth potential, long-term margins, and defensibility that these businesses possess. That kind of analysis is crucial to a valuation discussion.