My brother uses the silver threaded base layers and sprays down with scent killing sprays, and he has deer crawling all over him all the time. I've also used the scent killing sprays and the silver threaded clothes. I think they help a lot.
I have a set of carbon clothes, but I don't think I'll ever buy another set. I'm glad I bought them, because until I did, I always had this nagging wonder about how they worked. Personally, I think it's like Woods Walker said. Until you can put yourself in the same exact position with the same exact deer with and without the carbon suit, it really is impossible to know if the suit worked or not. Until we people can smell like deer, we'll never know for sure what does and does not work in the way of scent, including everything from scent elimination to scent attraction. The hard part with the carbon suit is that you'll never know how many deer smelled you and turned away before you saw them, and that would be a good test.
It's no secret that carbon suits don't completely hide your scent and make you "scent free". In my experience, the biggest buck I've ever shot came in under my stand while I was wearing my carbon suit. I had hunted that stand for two weeks knowing he was there and never saw him, but I wasn't wearing my carbon suit. The first evening I put on that suit and hunted that stand, he came out right under my stand. But deer do those kinds of things all the time. It could have been a huge coincidence. If I had to bet money on it, I would even go with the coincidence side of the bet. But I've had several encounters like the one I just mentioned, and I do think the suits help. I don't think they help enough to be worth the price, so I won't be buying another set of carbon clothes in the future, but I'm glad I bought the set I did and got to try it for myself.