The reporter covering the tea parties for the New York Times appears to think that "the rule of law" is some sort of exotic term of art invented by right wingers. Will Wilkinson notes that she's completely mangled what Hayek had to say on the subject, even though she brings it up in the context of discussing the Road to Serfdom, and its popularity with the Glenn Beck crowd.
It's been some years since I read the Road to Serfdom, but I don't remember anything that suggested that "the rule of law" referred to an "unwritten code" rather than . . . the rule of law.