Not all the tech companies that were hot in 1999 were like pets.com. Google and Amazon were amazing new things back then, and other companies like Dell, Sun and Qualcomm were also high fliers on the NASDAQ. (I'm old enough to have been an investor in 1999.)

I think the most significant difference between the 1999 bubble and today's situation is that today, many of the companies with astronomical valuations are not public. For example, if Uber's valuation tanks, some employees and some rich investors will unfortunately lose money, but most people will see little effect - if you have a 401-K invested in an S&P 500 index fund, you won't care too much. And the big public tech companies that are making money, like Google, Amazon, Apple and Facebook, probably won't be affected much if all venture backed companies disappeared tomorrow (except that their labor market would be flooded with developers). The NASDAQ might take a dip, but it won't be like 1999.