I like the women's only hours at the gym. It means I can actually get a chance to use the weights as opposed to not even being able to get a look in because they're all taken up by uni gimps who lift a weight, strut around with a protein shake for a bit, lift another weight, etc.
Although I do agree that there should also be men's only hours. At my gyms it's always just women on the treadmills so I bet some men wouldn't really want to be the only man on the treadmill, especially if you were a bit self conscious anyway. I think it's a great idea and would encourage newbies/the self conscious. When I first joined a gym 4 years ago I used to only go when I knew it'd be empty anyway because I didn't like the idea of exercising in front of big beefy men!