There is some of that. but for the most part (1) advertising revenues come from across industries, (2) startup revenues as a whole are fairly diverse coming fro

There is some of that. but for the most part (1) advertising revenues come from across industries, (2) startup revenues as a whole are fairly diverse coming from advertising, saas, transaction fees on rooms or rides and (3) most importantly I don't think Dropbox's value will hit critical levels because twitter's business model fails. its all a lot less speculative. multiples are high, but not the imaginary. most of the mature 2.0 startups are real businesses with a company value derived from revenue and profit.