When did you stop beating your wife? 
(IOW, what makes people think everyone must have some kind of religion, and thus be able to “change” it?)
… in case that diesn’t cover my answer to the actual question – answer is, of course, zero. No religion. Nothing to change.
Dani
I’m seeing a lot of denominational changes in this thread, but very few of the Judaism-to-Sikhism-and-back-again type conversions postulated in the OP. The other thing I’m seeing is a fair amount of religion-to-atheism progressions, but not so much the opposite (Pinkfreud and Metacom being exceptions). And so far, nobody’s willing to admit to changing religion more than twice, really. Does that equal a consensus that changing religions more than twice is weird?
One thing to keep in mind is that most of the major religions also have a cultural component, and many also have an ethnic component. So making a drastic change in religion (say, from Christianity–with no Jewish ethnic background–to Judaism) entails not only a theological shift but also a cultural shift as well. Adopting a religion with a strong ethnic as well as cultural component (almost all Sikhs, for example, live in the Punjab region of India) is an even bigger shift–if it’s even possible.
Changing denominations, changing from belief to non-belief, or changing to a religion that actively proseletyzes doesn’t raise those barriers (or at least they tend to be lower, when the exist).
Also, when considering how many people here have switched from religious belief to atheism compared to the opposite, keep in mind that atheists and agnostics are significantly overrepresented compared to the population of the US as a whole.
Metacom, you make good points. My Judaism-to-Sikhism example was only semi-serious (though I was sort of hoping someone would come along and have some totally implausible set of conversions, involving maybe the International Church of the Foursquare Gospel, Zoroaster, L. Ron Hubbard, Cthulhu, and radical Islam).
I was raised Catholic (and believed), mostly because I attended Catholic school from ages 4-14. Sometime around the eigth grade, the newest priest (who was mega conservative) really pissed me off (going on about “hate the sinner, not the sin”, adultry, using embryos in stem cell research, etc.), and I decided I was going to have to think a lot about my religion, if those things really were frowned upon in it. He’s also the reason I stopped attending church. I hated his homilies. (And so did 2/3 of my church. This is NY for goddsakes, I’d never met someone so openly conservative!)
For freshman year, I went to public school (yay!), where I’d never met so many athiests in my life. I went through a three month period of agnosticism (didn’t know whether there was a god or not), then decided I was deist. However, getting rid of those Catholic teachings has been such a problem for me, I’ve become kind of a deist/Catholic combination. Such as, I’m still going to pray and be my sister’s sponser for her confirmation, but I don’t believe God’s going to do anything because of it. He probably just laughs and shakes his head a lot.
On adultry - I should probably clarify, Catholics consider sex outside of marraige and (apparently) masterbation to be adultrous. I don’t see a problem with either of them, although I am very much against cheating on one’s spouse.
For the record, women can vote in my LCMS church. The only thing they can’t do is become pastors or elders (oddly, they can become missionaries though). Maybe we’re rebels. :eek: I know there’s at least one or two other progressives there (scandalous I know).
I grew up Catholic, then became not much of anything in middle school/early high school, then went to a non-denominational youth group with a friend, where it finally clicked. After that I ended up at a Baptist church in late high school, then nothing again when life knocked me off course for a while, and finally to the Lutheran church I’m at now, where I teach high school Sunday School.
So, if we’re not counting denominational changes, call it a big zero. 
The Catholic Church considers sex outside marriage to be adultery only when one or both of the parties is married to others. Sex between two unmarried people would be fornication. Masturbation is considered a sin, but it is not considered adultery or fornication.
I was raised a hard atheist. I converted to Christianity, which pissed off all my family, especially my Grandparents, no end. Within Christianity, I have made several denominational changes, to find out where I fit.
Btw, I wanna add that I regret not taking the opportunity I had during grad school to visit the Eastern Orthodox Church (or even the Evangelical Orthodox variation which later joined the Antiochan EOC). AND if I ever moved out near my brother, I’d probably joined Crystal Cathedral, which technically is (Dutch) Reformed (tho I am radical Arminian, I kinda get the feeling Schuller isn’t hardline Calvinist G).