The tipping point on the dotcom bubble itself was the NASDAQ market peak on March 10, 2000, the tipping point on the broader economy that the bubble bursting helped contribute to was the economic peak in March 2001 that marked the start of the March-November 2001 recession.

A number of government policies adopted before the bubble burst under Clinton and before the bubble bursting had worked its way into the public consciousness under Bush (safett net cutbacks, downward tax burden shifts, etc.) made the November 2001-December 2007 aggregate expansion after the 2001 recession and before the Great Recession have very poor distributional characteristics, such that much of it, especially the first couple years, felt like a recession for most outside of a narrow elite, which probably combines with the emotional impact of 9/11 to fix that late date as the beginning of the downturn, even though it was near the end of the downturn in aggregate economic terms.

I just know that when 9/11 happened, I had a day job and two side projects and by the end of the month all three were gone and I couldn't find another job for close to a year.

edit: and again, I'm in Phoenix so well outside CA/WA, etc...