BECAUSE I SAID SO
NOTE: This spoiler was sent in by Angela
The movie opens at a wedding. The bride, Maggie (Lauren Graham), her sister Mae (Piper Perabo) and mother, Daphne (Diane Keaton), are trying to set the youngest sister, Milly (Mandy Moore), up with a bachelor at the reception. As they send her off to introduce herself, Daphne warns her not to do her nervous laugh. Almost as soon as she starts talking to the guy, she breaks out into snorting laughter.
Cut to another wedding. This time, Mae is the bride and Milly has stolen away into a bedroom with a guy that she met at the wedding. She uses her cell phone to call her sisters because she thinks the guy might have "a bun on his hot dog". They are happy that she's found someone until they realize that the man she's with is married.
Further scenes establish the family dynamic; Milly has been unsuccessful in her romantic relationships and Daphne, widowed from an unhappy marriage, spends all of her time trying to steer her daughter into love, rather than focus on her own lonely life.
Finally, Daphne decides to place a personal ad for her daughter. She goes to a restaurant to meet the bachelors that have responded to the ad. After a series of interviews with less than ideal candidates, the guitarist from the restaurant band sits down to talk to her. The guitarist, Johnny (Gabriel Macht), wants to meet Milly but Daphne decides that because he's a tattooed musician, he'll just break Milly's heart. Johnny sneaks one of Milly's cards when Daphne is distracted by the final bachelor, Jason (Tom Everett Scott).
Jason is a successful architect and Daphne decides that he's perfect for Milly. She suggests that his company hire her catering firm so that the two can meet. Milly and Jason meet and start dating.
In the meantime, Johnny uses the business card to find Milly's catering business where he meets Milly and they also start dating. Milly is much more relaxed and natural around Johnny, but she's not sure if she's ready to be a mother-figure to his son, Lionel. Milly continues to date both men.
The situation escalates at Daphne's birthday party when Jason announces that he's going to introduce Milly to his parents and hints that he wants to be a part of the family. When it becomes apparent that Daphne is coming down with a cold, the sisters do rock-paper-scissors to determine who she'll stay with. Milly looses, so Daphne goes to stay with her while she recuperates. As they watch old movies, Daphne admits that she's never had an orgasm, because her husband never cared enough to take the time to please her.
One night, while Milly is out with Johnny, his father, Joe (Stephen Collins), comes over with Lionel because he's locked himself out of the house. As they wait for Milly and Johnny to return from their date, there is instant chemistry between Daphne and Joe.
Milly goes to dinner with Jason's parents and when he drops her off, Johnny is waiting and sees them together. He confronts her and is angry that she's been seeing Jason at the same time she's been seeing him. He breaks it off with her.
Milly is at Jason's when she overhears his mother on the phone saying that he met his girlfriend on the internet. Milly confronts Jason, thinking that he's dating someone else, but he reveals to her that her mother posted an ad for her on a dating site. Milly is angry and when her chocolate soufflés burn, she takes this as the final sign that Jason is not right for her, because she can't be herself and trust her instincts with she's with him.
Angry, Milly goes to Daphne's to confront her. When she arrives, she overhears Daphne and Joe having sex and realizes that her mother's having the first orgasm of her life. Milly leaves without letting them knowing that she's been there.
Milly goes back to her previously unhappy life and Daphne and Joe continue to see each other. By this time, Daphne sees that Johnny will make Milly happy and encourages Milly to try to win him back. Milly tries to see Johnny, but he won't talk to her. Finally, Daphne confronts Johnny and tells him that his pride is getting in the way. Johnny takes her advice and interrupts Milly's cooking class and gives her a big kiss.
The movie closes at another wedding. The three sisters are wondering where the bride, their mother is. They call Daphne's cell phone and interrupt her having sex with Joe. Finally, we see the entire family dancing, playing music and singing.