I was too young in the 90s-00s era, but couple companies (fb, twitter etc) with questionable valuations is a bubble? From the tales I've heard back then pretty much anyone could whip up a business plan involving the web and they could funded in millions and get to IPO within a year notice.
And even if there is a bubble right now, would it drag the entire US economy like it did in the 00s?
The problem I see right now is that we're not necessarily in a tech bubble so much as an unsustainable economic/financial/monetary/inflationary bubble. Most startups these days are very oriented toward frugality, efficiency, lean operating mode till they gain traction and self-sustaining levels of revenue (with a few exceptions like Color perhaps).
The problem is that much of the US economy from whence that self-sustaining revenue is currently being propped up with unsustainable deficit spending and inflationary monetary policy. The alternative is massive deflation, and is why the govt and Fed can't stop yet. But everything is balanced on a knife's edge, and if it collapses Silicon Valley may start feeling like it did in the last tech bubble collapse.
I like to think Startups 2.0 are more resilient to downturns by nature of more realistic and feasible business models and revenue orientation, but I don't know.
Based on reading around the past hour or so, I think the only ones set to lose right now are angel investors, the few wealthy with lot of money.