Secret Societies: lateral growth for character classes?

I don't how many of you picked up the Zorro comic book series by Dynamite written by Matt Wagner, but there's some fantastic stuff in there concerning the mythology of the titular character that I certainly wasn't aware of.

Of primary concern: La Justicia! This is the secret society that Zorro was inducted into, the one that taught him many skills and secrets that aided him in his fight against injustice. Furthermore, aside from the very demanding training and tests, each of the inductees are asked to take on a codename (El Latigo! La Fantasma! El Corte!) and wear a mask -- an attempt to right wrongs away from the prying eyes of the powerful and corrupt.

In Fading Suns, the Spanish-derived noble house known as The Hazat have a similar hidden tradition (inspired, no doubt by Zorro) known as The Domino. It is said that a noble who has been wronged, and has been deemed to have the will, integrity, and skill to make things right sometimes receives a domino mask and costume; an invitation to live up to the deeds and righteousness of past Dominos.

For fantasy campaigns and settings, the idea of a secret society need not be limited to those of villains. There can be various secret societies that are founded on high-minded principles and composed (mostly) of highly motivated, righteous individuals with skills and resources ready to aid the worthy adventurer.

This can be a slightly different take on the much-maligned 3E prestige classes, especially since the benefits of belonging to these societies can grant many non-combat related boons:

• sequestered artifacts
• obscure knowledge
• untapped resources

In addition, rising in the ranks of said secret societies (through XP and certain tests and tasks) will grant the PC abilities to reflect the training and knowledge and skills imparted to them. And it needn't be restricted to fighters: magic-users, thieves, and clerics would certainly be able to form their own secret societies if the need was great or the goal was noble enough.

All that remains is to construct them! It's certainly food for thought in the construction of Enigmundia.