A couple of good links to the current situation in the Bay Area.
Most of the tech stocks in the Bay Area are way over valued. Some are good companies but extremely overvalued and many out right garbage.
What I believed happened was the Federal Reserve created tremendous liquidity with it's QE (Quantitive Easing) policies. The Fed wanted to create a bubble and re inflate the economy and the stock market was it's vehicle for this . To do this it could not use stocks like consumer cyclical aka Johnson and Johnson it needed stocks or the money found stocks that could sustain outrageous PE's (price to earning ratios).
Hence the tech stocks. As far as public policy this was an ok thing, kept economy flowing, kept smart kids working and engaged with system that could be used for bigger things in the future. Now the winds of change seem to be blowing at the Fed as it is making sounds of how it wants to help the economy with a possible paring back of support, and with a new kind of thrust in the direction the elite want the economy to take especially with an array of geo strategic challenges in offing and the need to keep the dollar as the reserve currency a new tact seems to be in wind.