I never really used these sites until someone I met online asked if I wanted an invite. I was like hmm ok.
Then never used it.
When I was playing on a different online game, my alliance was talking about demonoid and a few other trackers and I was like "I have an account if you guys want invites" then everyone was like shocked asking how I got it. (thought this was about 6 years ago) it was only then, when I realized how rare it was (well, until now, seeing no one wants it and you telling me it's now considered a public tracker lol)