At GB i often read that this or that worked / didn't work. How do you know?! Have you just felt this or that way? You do not feel the effect of vitamin C either, does it mean it is useless?
Good point, this indicates that folks expect miracles / fast results from supps. This might be a naive view, but they paid many bucks for them, so it's understandable.
Regarding 'performance enhancing' supps, I've found out that crea gives me more power & endurance within a week and I get most of my protein from powders (confession right there) and regarding health supps, fish oil gives me better focus and a clear mind.