I believe that most individuals who become JW's as adults have two things in common:
(1) Limited bible knowledge, and (2) at an emotional pivot point in their life.
I was born into it - but the people I spoke to who were "converts" later in life all seemed to have these two common denominators.
Even though I was DF'd, I was still hooked by this religion and believed I was doomed to destruction until I started studying the bible independently of their literature (about 10 years after my DF). I was only realy "free" when I gained enough bible knowledge to KNOW they were not the truth.
I really feel for those who realize it is not the truth while they are still in - what a tough position to be in - knowing the truth and facing the possibility of loosing friends and family. I probably could not have made that decision, so I guess it's a good thing it was made for me!
I only wish the rest of my family was free.