Why not Nylon bushings?
Nylon is probably the worst of all worlds. When a suspension arm moves up and down it does not move only up and down but describes an arc. This means that, for example an inner track control arm bush will be required to flex in two dimensions at the same time. In this example a metal bush will allow this movement as will a rubber or POWERFLEX bushing. However a nylon bushing will allow up and down movement but 100% of the arc loadings will be transferred into the arm and the chassis. This causes arm flexing and can easily cause premature arm failure! Of course nylon has no vibration absorbing characteristics at all, so all vibration is transferred up the already highly stressed arm.