The system still works. Women traveling alone have to exercise more caution, but that's true of most activities in life, unfortunately.
The review system on couchsurfing is good. I'm male, so I'm going to have an easier time, but I've never had a problem with couchsurfing. I've stayed with and hosted a few dozen people.
Before I take ANY guest or send a request, I go over their whole profile, their reviews, their photos. Do them seem cool? Do they seem normal, no creepy vibe? Do they have reviews? Do the reviews go beyond "Jack is a nice man. He stayed with me two days."?
If they are "yes" on all counts, not only have they been safe, but they've been among the most interesting people I've met in 28 years on this earth.
Women should heighten scrutiny on all counts, and also check for "do they only host women?". Do they have even a SINGLE negative review or sign of creepy behavior?
Suffice to say, I've met plenty of women travelers who find couchsurfing a great experience, including while traveling alone. I'm not speaking out of male ignorance.