A common usage, at least for extract(), has been to allow an associative array to be passed to a function for use as named optional parameters, however, there is a lot wrong with dumping an array into the symbol table and then checking if what you want exists or not.
I have designed a pattern that allows an object to accept and address public level optional named arguments without the problems that could be associated with the compact()/extract() pattern. This pattern does require at least PHP 5.3 (uses late static binding) and overloads __get/__set preventing the child class from doing so.
