For what it's worth, gwern's findings are consistent with mine (see this thread). I'd rather restrict "brainwashing" to coercive persuasion, i.e. indoctrinating prisoners of war or what have you, but Scientology, the Unification Church, and so forth also seem remarkably poor at long-term persuasion. It's difficult to find comparable numbers for large, socially accepted religions, or for that matter nontheism -- more of the conversion process plays out in the public sphere, making it harder to delineate, and ulterior motives (i.e. converting to a fiancee's religion) are much more common -- but if you read between the lines they seem to be higher.

Deprogramming techniques aren't much better, incidentally -- from everything I've read they range from the ineffective to the abusive, and often have quite a bit in common with brainwashing in the coercive sense. You couldn't apply most of them to yourself, and wouldn't want to in any case.