I was hanging out fairly regularly (probably as regularly as I do now on MeFi) at the William Gibson Board and someone mentioned Metafilter. This was probably around 2004-2005. Checked it out and found it had everything I liked about the WGB and much much more. MeFi very quickly replaced my old haunt and has sufficed rather nicely since.
Life the universe and everything
I can't remember a specific moment but over the years this place has contributed to my real world education in a way my family never gave me. Hopefully not getting too much into the TMI territory here, but AskMefi has given me an education in human relations I never really learned in my fairly sheltered earlier life. I had fairly inconsistent messaging about relationships from a very early age and have learned, through my own experience and the experience of others reflected in years of questions something that's both incredibly valuable and almost entirely intangible at the same time. It's sat quite comfortably next to my entry into the world in the last few years and helped me consolidate the new models and structures I'm learning about how to throw myself into the world and not shy away from things that have previously felt too hard to approach.
(I've also found a place where I can talk about Doctor Who with people who are equally and possibly even more obsessed than I am :)