Whilst I too am sceptical about the claims of the alternative therapy industry, I have to say that taking glucosamine with chondroitin made a dramatic difference to my older sister. She went from being unable to turn on the bathroom tap due to joint stiffness to being able to turn it on easily within 6 months and she went back to knitting and crocheting - something she hadn't been able to do for the past 5 years.
I started taking it because I was getting the early signs of osteoarthritis in both little fingers and I have to confess the pain and stiffness have completely gone.
And then there's our 2 elderly dogs, both of whom were having great difficulty getting up off the floor, who are now able to do so quite easily. (the good thing about observing animals is that they tend not to fake their symptoms, so what you see is a genuine response)
So I think there is some benefit from taking glucosamine and chondroitin but more studies are needed.