Joan Rivers is known for her acerbic wit, a biting style that has had her criticize a healthy share of celebrities over the years.  But with the documentary Joan Rivers: A Piece of Work, the spotlight is on Rivers, an entertainer who has never been afraid to poke fun at herself (i.e. her turn Nip/Tuck).  Even at this stage of her career, Rivers still dreams of doing another talk show, a passion she developed filling in for Johnny Carson on The Tonight Show, a high profile gig which led to the short-lived The Joan Rivers Show.  The mouth that just doesn’t quit gives us the reason why her dream will probably go unfulfilled.  . (CLICK ON THE MEDIA BAR BELOW TO HEAR JOAN RIVERS)