I have spent a lot of time working around the world, and personally - while they are more difficult to find, I prefer the clothing free coed gyms.
A great deal of the time, women seem to treat the gym as a fashion show, which I find more distracting than if a woman was to be walking around in the buff. You have to be 18 to get into most gyms as it is, and we're all mature adults and have seen boobs and butts and genitals on the internet, so having a few less distractions at the gym and more opportunity to focus on the workout is so much more amenable.
Without the clothes, it's more relaxed, and since everyone carries a towel, people tend to clean up the equipment more, and generally speaking I don't have to deal with the fragrances and sweat on equipment where I would in gyms where clothes are required as people tend to be more careful to cover the equipment and wipe it down after they use it.
AS an adult, let's face it, I'd rather just zone out and put in my ipod than be distracted by the horrible crap people try to fit themselves into clothing wise at the gym, so removing it altogether as a distraction makes it so much easier to work out.
They're harder to find, but increasing in popularity especially in Europe and Asia. America's usually a couple years behind the times with modern trends anyways, so it will take some time to reach here.