Personally, while looking for something specific I have ended up reading all of the threads started at MousePad on 9/11 and the couple days after. It is interesting to see the raw reactions again, some long forgotten names (Lacrosse Boy!), and just the odds and ends of what comes up in a niche focused community.
This first hand account from the only NYC member we knew of, who watched it from her apartment window:
Interesting to see CP noting the new security bag checks and that they seemed nice. Marla (aka HBTiggerFan) warning us all that an email that 9/11 was predicted by Nostradamus is a hoax, etc. Being reminded that even I wasn't so curmudgeonly to publicly resist the idea of using flags as avatars (though privately I continued to think using the flag as a display of anything meaningful to be silly at best). The behind-the-scenes discussion of how MousePlanet should cover it.
I'd completely forgotten about the moment of silence (after emptying all rides, stores, and offices) and parkwide playing of God Bless America at the park the next day.