Let's not even get started thinking about the warlike Xambia in the New Guinea highlands, or the guevedoces of Dominican Republic (http://www.usrf.org/news/010308-guevedoces.html).
The boundaries between genders, even at a physical level, seem pretty porous.
http://linuxmafia.com/faq/Essays/marriage.html
"In particular, in 1967, Polish sprinting champion Ewa Kłobukowska was disqualified (and banned from professional sports!) for being (probably) XXY on the basis of failing the Barr body test, as was Spain's hurdler Maria José Martínez Patino for being XY (CAIS) in the 1980s. Worse, during preparations for the 1968 Grenoble Winter Games, Austrian skier Erika Shinegger was genetically tested, determined to be XY (probably CAIS), and disqualified. This was a great shock to all three women, who were raised female and had no reason to think otherwise. (Erika subsequently did have a sex change, and is now Erik. Maria's competitive eligibility was reinstated in 1988. Ewa retired, married, and gave birth to a son.)"
To me it seems pretty solid, compared to pretty much anything else you can tell about a person's biology just by looking at them.
http://www.texastribune.org/blogs/post/2010/may/04/tribblog-...