Angus Croll covers the new 'use strict' operator introduces in EcmaScript 5th edition and how to get started using it. He offers a set of unit test to see how well supported strict mode is in your browser.
Douglas Crockford explains the new strict mode introduced in the 5th edition of ECMAScript. It is an opt-in mode that repairs or removes some of the language's most problematic features such as: function scoping, implied global variables and global leakage, read-only variable failures, octal defaults and function arguments.