The barn I board at currently separates genders. I just watch how the girls act when they are in heat and it made me wonder. People kind of seem to be prejudice to the fact that I had a mare - it wasn't difficult perse - but you could kind of tell they would rather she be a gelding, well that is, until they met her. Most of the time they'd say "sure, you can board her here, but you better be prepared to fix some boards." I think I'll try it out as an experiment, and in the future, I'm not opposed to mixing, I guess I'm uneducated about it right now. It's really just a matter of wanting my horse to have a large turnout with horses I know she'll be able to live in symbiosis with.