The forum UID ties in with the LFS UIDs, from what I understand. This means that the first non-developer account is http://www.lfsforum.net/member.php?u=2.
I've no idea if that was the first purchase though.
That is quite interesting because he called me in 1999 and said, "Hey Mike, I'm thinking of programming some kind of PC game" and I said "Why not make a racing game? You could try to make it, like, ultra realistic or something" and he said "That's a good idea, thanks man" and I said "Like no problem".