Well shit...your post made me realize I've never really changed my mind on any non-empirical issue - although I have had blank spaces filled in, of course.

Would you consider EY prominant? He is here, at least. Here is a description of his conversion from the (I say surely false) belief that Aumann's agreement theorem would cause rational agents to behave morally to the (I say surely true) belief in No Universally Compelling Arguments. He did it at age 18 and wrote essays on it too, so its not like he just filled in an empty space - he actually had to reject a previous belief, which he had given a lot of thought about.

http://lesswrong.com/lw/u2/the_sheer_folly_of_callow_youth/