ETA: _This Film is Not Yet Rated_ includes a fair amount of footage from films which were unable to get R ratings. It also includes a few montages of contrasting footage from films which were able to get R or PG-13 or whatever ratings. In general, the former were largely inoffensive to me (altho the puppets having kinky sex that involved defecation was moderately gross). I couldn't watch the montage of violence against women that made it into movies rated R or less.
While not nearly as funny as the documentary _Fuck_, this is way more worth the time it takes to watch. I highly recommend it; you can get it through Netflix. I'm not sure where else you could lay hands on a copy, other than buying one.