It was with great interest that I read about Caster Semenya, the South African runner who was born intersex. Being a science-nerd, I have to point out that human genetics is a lot more complicated than most individuals think, and that the binary gender model, while applying to most people, is not sufficient to explain the full range of human sexual phenotypes. When one intently researches human genetics, one encounters individuals with XYY genomes, chimerae who have two separate genomes, and intersex individuals of various genetic origin.
My personal feeling is that the binary model of men's and women's athletics may be outdated. Perhaps a competitive model which groups cohorts of competitors by testosterone levels and muscle mass without assigning individuals to a particular gender is the best solution. I don't think, though, that the conservative International Olympic Committee would be willing to do that anytime soon. By not separating competitors into a female/male binary, perhaps coverage of women's athletes wouldn't be so damn sexist.