No, ex-gay therapy does not work, and is in fact, rather pointless. Being gay is not a disease. Nor is it something you can turn on or off. Sending an individual to ex-gay therapy can lead to that individual repressing who the actually are and can increase their likelihood of having mental issues down the road. As a society, we'd be far better of welcoming gays into our community rather than trying to force them into a farcical therapy program.
Even if you could cure homosexuality you wouldn't do it the way these idiots think you can do it. "Pray the gay away". OK then let's "pray the cancer away", "pray the asthma away", "pray the Parkinson's away". And then it's not even a disease and they approach it like it is, so of course it doesn't work. Maybe a "it's not a disease and it isn't wrong but we're just here to offer help to people who want to change for the heck of it" program would work. If they do that we should also have ex-straight therapy.
All studies of ex-gay therapy have shown that it doesn't work. For one, homosexuality is not a mental disorder or deviant lifestyle. The important part here is that there is no evidence that sexuality can be changed or manipulated. Since it is not needed or functional, it should be abolished.
The best thing for the gay community is for people to accept them as they are. It is how you are born and you could no sooner reprogram someone to be gay as you could reprogram your eye color. Life is made of lots of different kinds of people and they should all be tolerated and respected.