I found MeFi during the Kaycee Nicole debacle, but was unable to read the site, never mind post to it, during that time. Flash-forward to September of 2001, after the planes hit the WTC. I joined and first posted in a thread about Laurie Anderson.
Most recently, the Clarence Clemons post.
Tough call. I think just reading the site and being impressed about how intelligent these people are (and how many assholes are content to let their assholery just hang out). I always feel like the dumb kid at the cafeteria table, humbled by so many of the other folks.