Zack and Miri are two lifelong platonic friends who make an adult film to pay the rent of their apartment. With their friend Delaney, the couple set out for auditionees for their porn film, but in the process of filming, they realize they feel more for each other than they had before.

When Mabel catches her husband flirting with their maid, it leads to a sharp dispute. As part of making up, the couple decide to take a walk to the park. Nearby, another married couple have just had a similar domestic squabble, and they too go to the park together. But at the park, both men find it difficult to avoid getting themselves into further trouble.

New York. Rebecca (Moore), an actress, is crushed to discover that her marriage may be falling apart. Her husband Tom (Duchovny) leaving long-suffering Rebecca to pick up the pieces of their relationship. Rebecca's brother Tobey (Crudup), meanwhile, is in a long-term relationship with Elaine (Gyllenhaal) that has begun to turn sour. Both couples are spoiled and bratty.

Eddie is forty, owns a sporting-goods store, and is still single. After watching his ex-fiancée walk down the aisle, he meets Lila, an environmental researcher, who seems too good to be true. Pressured by his father and best friend, Eddie pops the question and marries Lila after only 6 weeks. However, as he almost instantly discovers, his new bride is a nightmare with more baggage than he can handle. She's immature, foolish, a monster in bed, owes a tremendous amount of money to various sources, and as it turns out, is only a volunteer and doesn't actually have a job. While on their honeymoon in Cabo, Eddie meets Miranda, a down-to-earth lacrosse coach who is visiting with her family. Sparks fly, and Eddie falls for her. Now comes the tricky part of breaking off his marriage to crazy Lila, all while keeping the truth from Miranda about why he's in Cabo in the first place...