The 4 piece bonus and 6 piece bonus of Rune of Perplexity are supposed to add 15% confusion duration each, for a total of 30%. Currently, neither bonus works, and a character using Perplexity runes does not have increased duration at all. It does not work for character skills or for the confusion proc applied by the runes themselves.
I know Perplexity runes are pretty hated right now, but as a Mesmer, that confusion duration was the big selling point for the runes, since I have more reliable confusion skills of my own.
Paldirac / Frajad @ Gates of Madness
Primacy @ Zuluhed (WoW, retired resto shaman)
Theory @ Azphel (Aion, retired control spiritmaster)