To me, the obvious sign of the bubble isn't the high valuations, but the asphyxiating red tide of MBA-culture people who are in technology for all the wrong reasons.

They're an invasive species. They come in during bubble times, compete successfully for attention and funding, because they have superior social polish (and, more importantly, can exploit the "just like me" bias of chickenhawking VCs) to the real technologists, build a self-referential junk-pile of nothing, and then leave just before the silly bubble-world they've created collapses.

Then real technologists get a few years of relative calm and meritocracy (although there's not nearly as much money in it, then) before the cycle repeats.

Technology is incredibly rewarding and I wouldn't want to be in any other career, but it's hard and you gotta be real to get any good at it. It takes years of realness-- hard work (often unrecognized) that kicks your mental ass-- just to get the basics. When people who aren't real try to come in and get the rewards-- Harvard MBA CEOs who don't even understand linear algebra setting themselves up as "data whizzes" because they were able to hire smart people-- it's irksome.