I've never used it personally, but I know a lot of other ex-pats who wouldn't travel any other way. Of course there are safety concerns, but I think that's really rarely a problem. I've met a lot of people who were staying with friends of mine through Couchsurfing and they all seemed like really nice, interesting people. I think it's quite common for women to only want to stay with other women, but that's understandable. There are also a lot of CS parties and gatherings, which normally just involve all couchsurfers from the same area meeting up, but sometimes there are really big parties which will have couchsurfers travelling from far and wide. I think that's definitely a bonus of becoming a couchsurfer.
After you've stayed with someone you can give them a reference, which will show up on their profile, so it's easy to see who would be good fun to stay with and who's had plenty of experience hosting.
I think another bonus of travelling through couchsurfing is you get to see the areas you travel to through the eyes of a resident rather than a tourist. I think that's really great because you'll get to see all the best places, bars etc. rather than just areas you stumble across or that are advertised as tourist attractions.