I don't know if I can go so far as to say these forums have changed my mind on anything, since I was pretty much a newbie when I came here, and had hardly any preconceived ideas to be changed. However, I have certainly learned a lot. In fact, almost all of my traffic education initially came from here. I found when I finally took the LAB Road I course a few months ago that I already knew most of it, thanks to this forum.
I do continue to go back and forth on certain issues based on what I read here, especially bike lanes. Since I don't have many where I ride, I've never relied on them and have often leaned towards favoring the anti-BL arguments. However, I'm still a little on the fence, and in fact may be moderating my view a bit. It's still a "work in progress".
Probably the biggest thing I've learned is that riding conditions vary wildly with geography and it's difficult to make blanket statements about anything!