I've used it a long time ago, in 2011, for 4 times, when I was living abroad. I didn't have any problems. I liked very much the experiences.
In three of them I was with a friend. Two of the hosts went out with us and showed the city, and just one of them asked to pay for a drink and to cook a simple dinner in exchange. One of the house was not so clean, but I didn't mind so much.
In the other experience I went alone, but I stayed in a girl's house and I had the opportunity go out and meet her friends and mother.
But I think for women is more difficult to find a safe place. Nowadays I prefer to use AirBnb, but you have to pay. And I prefer a couple to be host.
What I can say is that no matter what you choose (CouchSurfing or AirBnb) you should read carefully the comments of other guests and the host's profile. Try only hosts that had guests before. And people have their own way of living and different culture. Be open to learn more about it.