Honestly, I can't count them all. Perhaps hundreds but at least many dozens. As Simon said, everyone who participates on boards is part of the process.
In debates, my "specialty" (which I've often been vilified for doing) is, basically, to bash them over the head (verbally) with a baseball bat and evidence to get them thinking again. Too many people to count have told me that is exactly what they needed, but of course, there are many different kinds of people and many different kinds of JW entrenchment in those people.
In my thread topics I employ lots of irony, parody and sarcasm in order to have dubs see the foolishness and absurdity, not only of their religion, but the absurdity of most of the Bible.
One thing that I didn't see mentioned in this thread is a sort of "trick down" effect. There was a poster who went by "Pioneer For Life" and he was just that, or so he thought. He did his best to stand up against the evidence and slowly realized he could not. He resigned his positions and left the religion. Several years later he called me and told me he had helped get out over 20 members of his family and friends.
So remember, if you can help just one dub get free and that dub can do the same and so on, it makes a huge difference in the quality of the rest of those people's lives.
Farkel