Interesting thread. When I think about it, my parents present two of the classic examples of how people get sucked into the JW religion:
My mother's first husband died tragically after they were married only two years (fell off a building as a construction worker). The witnesses were coming around during the same time, and once that happened she just threw herself into the faith. She was young and incredibly vulnerable from the pain and loss. In fact, one of the stories she will tell is about the night after her husband died and she was crying herself to sleep: in the middle of the night she heard his voice calling her by her name. Since she had just been introduced to some of the basic JW teachings, she interpreted this as being the demons trying to get to her when she was weakest. This, of course, merely reinforced her belief in Jehovah and the WTS.
My father was involved in drinking and drugs, and had a lot of issues with his dad abandoning him when he was a kid. The JWs came around and he attached himself to a father figure who started to study with him. He kept screwing up (drinking, women, etc.), but this JW father figure kept him in line and provided him some sort of discipline he needed. He got baptized, and soon thereafter married another sister. The marriage didn't last the honeymoon. A while later, he married my mother. And that was that.
When I look back on it, it's really rather pathetic. Two people struggling with life and very weak, taken advantage of by people who meant well, but it was really just that discipline, structure, and social support that they needed.