It's a somewhat unremarkable story. Back in 2001 or so, when blogs were sorta new and everyone had one and everyone linked to everyone else, someone (I'm 99% sure it was the user known as frykitty) linked to something on Metafilter. I checked the site out further and signed up, since it was free at the time.
Impossible to say
Like the internet itself, I can't think of any one moment when I felt "wow, this is amazing!" It just sort of crept up on me over the years until it became an integral part of my life, a tool that is always there that I can rely on for certain tasks. I would get by without it, of course, but I would miss it.
This thread stands out as a big step, when I made the leap from fake internet people to real people. Not only did a human offer to send a physical object to me, but by that time I trusted these people enough to receive a food product from a total stranger and allow my wife to consume it. She didn't die and I learned that "internet people" are no different than, you know, people. With shipping, those pickles cost me about $45.00. Totally worth it.