These were created just after DiscoStu's extended campaign of stupidity, both in the chatterbox and in nodespace, in January 2001. While there had been trolls before, DiscoStu was the catalyst for the creation of many of the controls we have on the site now; I think users today would be surprised at how minimal the infrastructure was in 2000.
As far as when the site was opened to the public: I became a user Feb 17, 2000 in order to ask a question, but I had known about the site for some time before that because a "slashbox" for it appeared over on SlashDot (in fact, I was rather annoyed with myself later for having waited so long to join; I was no longer cool for being early!). pschoonveld was a real user, and not a part of BlockStackers, so far as I am aware; he answered a question from CmdrTaco on December 2nd, 1999.
I think that there was a certain ebullience about the site itself, and the community, early on that we no longer see; you were much more likely to see technical marvels like My 2 cents worth, for instance, and creative posts like Life at the Monastery. Chapter 1. Things have since settled into a routine, which I think was inevitable.
I also think tilly is overly generous with Alex the Serb, who was a complete ass.