Adobe has released Flex PMD.

FlexPMD is a tool that helps to improve code quality by auditing any AS3/Flex source directory and detecting common bad practices, such as:

Unused code (functions, variables, constants, etc.)
Inefficient code (misuse of dynamic filters, heavy constructors, etc.)
Over-complex code (nested loops, too many conditionals, etc.)
Over-long code (classes, methods, etc.)
Incorrect use of the Flex component lifecycle (commitProperties, etc.)