Considering that some substances are banned for use by athletes is an indicator that they work to enhance performance, even something as widely used as caffeine.
I think the question is whether you should take supplements, and what is the reason for it.
I personally tend to agree with those who say that you should eat a balanced diet which provides all the encessary nutrition. Having said that, I also take a multivitamin because I know that I do not always do that.
When it comes to supplementation for enhance performance, I leave that question for everybody to decide for him- or herself. It never crossed my mind but I can see why people would be tempted.