This is a fact admitted at several points through this film. And it's an important thing to bear in mind when considering the film, because the film is not the joke. The film is *about* the joke. It's a documentary. It deals with far more light-hearted matter than the average documentary, but it's a documentary nonetheless. Yes, the joke is told frequently and in various ways throughout the film. But in and of themselves, only about four incarnations of the joke are worthwhile. Billy The Mime's version is inspired, the guy who does it with playing cards is clever, Gilbert Gottfried's is a masterpiece of saying precisely the wrong thing at the right time, and Sarah Silverman's first-person rendition lies perfectly between deadpan hilarity and abject horror.
The value of the film lies in the story of the joke. And in this regard, it stands as one of the funniest films ever made. The joke isn't something to be told at the dinner table. It's a challenge, told by comedians to comedians. And this is where the hundred or so comedians in this film come in, to tell us their own stories and experiences about the inception and reception of it - and of course, to do this it becomes necessary for one or two of them to provide their own interpretations. And so it goes on.
As a comedy, it's not that funny; it is, in a very literal sense, a one-joke movie. As a documentary, it's genius.