I was just reminiscing over on Facebook (where lots of folks were putting up their "where I was" remembrances from 9/11) about how amazing LiveJournal was on that day.
There were only about 325,000 LJ users back then (about 1% of current LJ accounts ... I triangulated the number from a couple of folks on my friends list, one who joined on 8/13/2001 - #312314 and one who joined on 9/16/2001 - #346952) but the level of involvement and communication was incredible. Everybody was trying to connect with friends in New York, help families of people in NY and DC connect with their relatives, putting up as much of the latest news as possible, etc., etc., etc.
You have to remember, that the phone system was pounded by the attacks, with everybody wanting to connect, and a lot of the time all there was were busy signals. LiveJournal was up and running, and so users here turned it into an alternative, with phone trees reaching out to the rest of the world.
One of the most gripping stories from 9/11 of those on my friends list here was that of banshee who wrote that morning: "if i were on time to work today, i'd have been in the world trade center when the two planes hit." ... she was working in the photo end of the fashion business back then and took a subway that let off right under the WTC. What was even more creepy was her story, a couple of years later, of getting a pack of film delivered to her that she had dropped off at a film developing place in the lower concourses of the WTC. The film had somehow managed to be connected to her, and when they dug down that far, somebody thought to deliver her prints.
Anyway, 9/11 is unshakably linked with LiveJournal in my mind ... and I'd guess with a whole lot of the "early adopters" around here. What happened on that day, and the ensuing weeks, certainly opened up a window on what the web has become with instant participating in news delivery.