I feel like I have to start out by saying that this is an amazing film and that part of the reason I wanted to see this film is because John Cameron Mitchell is the director. He directed another of my favorite films Hedwig and the Angry Inch. Shortbus is essentially about several individuals and the relationships they develop. The name Shortbus refers to an underground club that they all frequent that is part poetry/music/film house and part sex club. The characters are all trying to find themselves with issues ranging from a young man who is depressed to a woman who has never had an orgasm and is a couples/sex counselor to a woman who has never had a stable relationship. The plot is really interesting and the relationships between all of the characters feel genuine. This film is essentially about the search for love. But the reason this film is unrated and hence may not be on everyones list is that there is a lot of sex in the film. The sex is always within a relationship and is "real" sex, it is not the typical porno style sex that seems to crop up in all American films. These are real people having a real connection and having real sex. There are a variety of different sexual acts from a straight couple having sex to a homosexual threesome to scenes of masturbation. Again, this is an amazing film. The development of the relationships is very well done, the cinematography is amazing and the direction is great, so if you get a chance to see this film, do it.
UPDATE: So I watched the extras and they are also very good. There are a lot of really interesting things bout how this film was made. They also talk about how the sex is filmed and that most of the orgasms that are shown are genuine and not faked, yet another difference between this film and most American made movies. I can't remember this happeng with any other film that I have seen, but even the deleted scenes were all great, I really wanted them to be in the film as well. Normally, for me at least, there is at least one or more scenes that I think yeah I really understand why that didn't make the cut, but with Shortbus I think any of the deleted scenes could have been added and it would not have hurt film. I also have to add that originally one of the characters plays the personal assistant to the Bush twins and there are some great scenes of him on the phone with the president, Jenna and not-Jenna.