I've heard that some Jews consider that a person has not so much converted (i.e. changed themselves), but rather has realized that they *are* Jewish, and go through a
mikvah and other stuff simply as a way of acknowledging this newly discovered fact.
I'm rather fond of this way of seeing things. I'm not sure whether I'm a Jew or not -- more of my religious education was Jewish than anything else, but I was never bar mitzvah (or confirmed in any religion). If I should decide that I really am a Jew, I certainly won't refer to it as a conversion.