Frankly, I think it's a little creepy to go try stuff on in a fitting room with women and girls running around. I suppose it all depends on how the fitting room is configured. In stores with men's fitting rooms, this is not a problem, although it does require walking clear to the other side of the store just to try something on.
Thought I was done with this, but...
I guess I don't understand why it is creepy unless the people themselves are creepy. As stated earlier, I have been to many many stores, such as Old Navy and the Gap, and even newer Targets where they only have one set of fitting rooms for both sexes. And stores like Forever 21 which recently started selling men's clothes didn't build an all new dressing room area, they just keep using the same ones for everyone. These aren't mom and pop shops, these are major corporation who seem to have no concern about having men and women try on clothes in the same general space.
In just about every dressing room I've ever been to, each person is given their own little stall where they can go and privately try items on. And on 95% or more of these places, these stalls are always locked and you need a SA with a key to open them, even if you step out of them in order to check yourself out in the bigger mirrors outside or to show your outfit to a friend, you need someone to open the door for you again. In some instances these aren't locked doors but curtains, and usually open up right into the store or there's a fitting room attendant who stays nearby, so the chances of any hanky panky going on in them are pretty slim.
I recently tried on a skirt in a women's clothing store called "Charlotte Russe" that is in one of the local malls, and I used their fitting room. The layout was identical to the ones I have seen in the above mentioned stores, there were six stalls that could only be opened from the outside with a SA's key. The only difference between this fitting room and the ones at the Gap, were that only women's clothes were sold in the store.
Ok, there are rare cases where the rooms are more communal, such as I remember in high school going into a store in new york called Strawberry with some girls and they said the dressing rooms were open stalls plus the ceilings are sort of mirrored so you could pretty much see everyone else dressing while you were. Obviously in instances like this, if no fitting room was available to men I would not be upset by not being able to try something on. But this is the exception and not the rule.