I know this is somewhat of an old topic to bring up; I recently watched a video about Caster Semenya (the South African  middle-distance runner who won gold in the women's 800 m race at the 2009 World Championships), and it got me thinking about whether or not she should be allowed to participate in a women's only sports competition.  
 
In the video, the scientists that ran tests on Caster say that she has a higher amount of testosterone than normal women do, which give her an "unfair" advantage in athletic competitions.  While I agree that this does give her some advantage, she did not acquire these levels through artificial means; she was born this way.  While the IAAF may try to convince themselves and others that other athletes in competitions do not have any advantages over each other, they are misleading themselves:  everyone has certain differences in their genetic makeup as well as physical manifestations that allow them to do certain things better than other people.  Some people have larger lungs... some people are genetically programmed to have a different amount of slow-twitch to fast-twitch muscle ratio, and some are taller than others... hell even some sexual characteristics in some people are expressed more in some people than others... some have XY, some have XXY, and some even have XYY, etc (there ARE varying degrees of maleness and femaleness).  When it comes to the expression of our genetic information, our phenotypes (such as eye colour, skin colour, and ratio of hormones) are  expressed on a varying scale.  Caster is just on the extreme end of the spectrum.
 
To exclude her from participating in her sport just because she's an anomoly, however, is to do her an injustice.  Athletes with extreme characteristics are celebrated in other sports (eg. Shaq and Yao Ming), so why shouldn't she be also?  She IS a woman - she does have female body parts - her hormones are just in a different ratio than normal.  If she is to be excluded solely on the basis of her testosterone levels, should we have tiered competitions amongst athletes based on hormone levels now?  Athletes are more than just the sum of their parts.
 
In any case, Caster's courage and bravery in facing her critics (criticizing over her sexuality/gender, ffs - can you imagine what it'd be like to have people ask you.. are you a guy or a girl?) head-on while remaining true to herself and her community is to be commended.  To her critics, she asks, "If someone was born the way she was born, or he was born, are you going to go and blame him, or are you going to blame God?  Who's fault is that?  Nobody's."  For someone that young to have that kind of confidence is inspiring; she didn't ask to be put into the spotlight like this... she just wanted to be the best athlete that she could be.
 
The IAAF did, in the end, clear her to return to competition, after she was withdrawn from competition.  Recently she won silver in the 2011 World Championships, and dedicated her medal to Nelson Mandela.