Some more details would make this post informative rather than simply an arcane inside reference.
January, 1990---Operation Sun Devil goes down, where the Secret Service arrest a bunch of teenagers who have illegally accessed computers and charged with disseminating internal AT&T documents describing how 911 works. The era of the 80s "hackers" ended.
March 2000---the tech stock market crases. The Internet craze pretty much tanked at this point.
None of this is anything I consider "arcane inside references" but hey, I'm into computer history.
http://en.wikipedia.org/wiki/Eternal_September
This isn't a big date technologically speaking, but as far as the social history of the internet goes, it was huge. I suspect it's one of the big reasons AOL was so demonized. (There are obviously many others.)