Answer
Not to be flippant, but if they are secret societies, it would be a secret, wouldn't they?
Skull and Bones is the most famous of "secret societies" as is the Masons. The Masons make no secret of their membership, with their car tags, and marching in parades, etc. Bush, John Kerry, to name a few, were members of Skull and Bones at Yale.
Arnald Schwarzenegger has been rumored to visit the Bohemian Grove. According to various sources, that's where he was tapped on the shoulder by Karl Rove to run for Governor in the Californian Recall election... and the rest is history.