Continuity mistake: When Katherine Heigl and her sister are having a fight, her sister throws a portable phone onto the couch. The phone goes from just being visible behind one of the cushions to completely vanishing a few seconds later after the "Bridezilla" rant.
Continuity mistake: In the final scene of the movie when Jane gets married on the beach, you see guests arriving and Tess is handing out programs. She hands a program to a blond girl with a brown polka dot dress. In the next shot, we see Tess talking to George and the same woman arrives again and Tess hands her a program again.
Continuity mistake: In the argument in the car in the rain, Kevin has a seatbelt on, but while accusing Jane of being in a creepy love triangle, he has no belt on. When he says "Nice Jane," he has a seat belt on. It is off again when Jane says she is thrilled about the boss and sister marrying. It is on again at the road sign where Kevin doesn't have Spidy vision. When Kevin checks for a cell phone signal once the car stops hydroplaning, the seatbelt is over his collar but when he snaps the cell phone shut, the collar is over the seatbelt suddenly.
Continuity mistake: When Jane is tying George's tie, the part around his collar goes from being seam-side out to in to out again between camera angles.
Continuity mistake: Kevin and Jane are performing Benny and the Jets on stage. There are two blonds in the crowd, but the one on the right sometimes waves a cell phone or a glass of water, depending on the shot.
Continuity mistake: When the boss is proposing to the sister, one of the men who is holding the fabric sign has it scrunched up in one corner. He then drops the fabric so that it is hanging straight, but then changes between hanging straight and scrunched between shots.
Continuity mistake: After arriving home depressed from reading the article Kevin wrote in the journal, Jane is seated on her couch beside a pillow. You can see the flower in the lower corner of the pillow, but when Tess is screaming about bridezilla, Jane has moved over and you cannot see the lower flower - but later she has moved for the viewing of the flowers again when Tess leaves.
Other mistake: In the end credits, the pseudo-newspaper text surrounding James Marsden reads "The best man was Kevin Doyle's long-time friend and colleague, Trent, who has [James Marsden] The best man was Kevin Doyle's long-time friend and colleague, Trent, who has recently taken over." The part before the actor's name is repeated immediately after.
Continuity mistake: When Kevin tries to convince his boss in her office that he wants to do some work using Jane's journal, the pencil in her hair sticks up more sometimes.
Continuity mistake: When the friends are at yoga, Jane's hair at the side bangs has fallen out at each side, but then it is all back again in some scenes.
Continuity mistake: When Jane and Kasey are in the yoga class, Kasey goes from not wearing a bra, to wearing a bra.
Continuity mistake: George and Jane are at the boat house and when they arrive there are no boats in the water behind George. Then a lot appear and from then on there is no continuity of boat positioning in the water.
Continuity mistake: When Kevin is photographing Jane they both mention 27 weddings and dresses. On her wedding day Jane's states that she put on her 28th dress. Since the goth wedding occurred after Kevin had photographed her, and we know Jane is highly detail oriented, she would have told Kevin she had been in 26 weddings and was about to be in her 27th. Given all the details she readily provided about the other gowns it seems odd she didn't mention something about the goth-themed wedding.
Continuity mistake: Jane is modeling the yellow dress with red flowers and Kevin has the camera in his right hand but when he says "Oh my God!", his right hand is free to cover his mouth. Then the camera is back in his hand to take the photo. Later when Jane is sitting in the red dress talking with Kevin about things she has done for people as a bridesmaid, her necklace that was off center moves to the center. But when she says "I am Jesus" and then is back off center again.
Continuity mistake: Kevin has taken the photo of Jane in the olive green bridesmaid dress but his pointer finger changes position high and low on the camera as he turns it to Jane and back.
Continuity mistake: Kevin and Jane arrive at the bar, and after Kevin announces the pay phone is dead, the bartender sets a glass down and puts his hands on the bar. But after Kevin places the scotch order, there is the sound of a glass being set down again, and a small piece of the serviette shows. After Kevin and Jane dance to Benny and the Jets, Kevin helps Jane off the stage and Kevin admits he cried at the Keller wedding. Some sweat is shown on his neck, but when Jane grabs his neck to kiss him, his neck is dry.
Continuity mistake: At the ballpark, Jane, Tess and George sit down on a concrete bench. A few moments later, when George gets up to play baseball with Pedro, he sets his food down on the concrete bench and you can see that the two women are sitting on a black foam pad that wasn't there before.
Continuity mistake: When Jane is wearing one gown (from Suzanne and Greg's wedding), while carrying another in a bag, she hails a taxi and affixed on its roof there is an illuminated advertisement panel and its number is "9Z66". However, in the next two shots the ad panel has vanished and the taxi's number is now "8Z30". (There is a missing shot which can be seen in the deleted scenes. Still a mistake, but there's the reason.)