Are you on crack, Steve? I know members of my family (for an example of completely out-of-the-SF-loop) who would be able to identify Darth Vader, but if you meantioned Darth Sidious to them they'd think you got his name wrong, or that you had a speech impediment.
Maybe more children uder the age of ten might know who Sidious was ahead of Vader, but no-one else older than that has even heard of him (aside from SW-junkies that hang out on internet fora. )