The sith thing has come up before, I believe it is only mentioned in the ANH novel. Whether the intention was for this to be an organisation, or just a throwaway name who knows...

Personally I'd love to see the 'Sith' gone from the PT. If any Jedi can just fall to the DARK SIDE without necessarily buying into this secret organisation it makes the idea of turning bad far easier and much more tragic.

Any of us can become evil, angry or violent, we don't necessarily have to join an organisation to do so.