In Michigan, the law is "Stay Right, Left to Pass". I saw a sign stating this on I 96 last week. One could assume that this would apply to any road of 2 or more lanes in the same direction.
I have to use the right lane when in my work vehicle but it would be nice if people used the passing lane as intended instead of parking there going 72 when other lanes are open.
My favorite sticker is "Unless you are a hemmoroid get off my a$$!!"
