When Peter is talking to his stepbrother in the kitchen, (before he goes to Hawaii) the cereal in the container on top of the refrigerator changes position several times as does the container after Peter talks about Sarah giving it to him.
When Chuck is explaining his Hawaiian name Kunu to Peter, he said that he just typed Chuck into a program and it came up. The actual translation for Chuck is Kukaki. Kunu is not on the list of Hawaiian names.
When Peter and Brian are talking on the web cam Brian starts doing a dance pretending he is in Hawaii and Peter says "they're not Native Americans" But Native Hawaiians are Native Americans they can even receive Native American benefits under the Native American Programs Act.
In the scene where Peter meets Kemo on the beach and is given a beer, when the camera is facing Peter from behind Kemo, the bar towel is missing from Kemo's left shoulder. But when the camera is facing Kemo and behind Peter, it is there again. There are 4-5 alternating shots showing this mistake.
When Peter and Rachel are sitting on the beach talking at the luau, her ex-boyfriend and the buffet waiter walk behind Peter and Rachel. When Rachel starts screaming at him, the two men are walking towards her.
When the group are in the restaurant and Sarah says that the movie they are discussing was the right choice for her at the time she downs her wine. The shot then cuts to Peter and Rachel, and the wine bottle is visible throughout. When the shot pans back to Sarah her wine glass is half-full again.
When Peter and Brian are talking in Peter's kitchen. Clearly from the scene the two of them are alone in Peter's apartment. Although, during their conversation one could see a reflection in Peter's "stay fresh" cereal box that a door opens and then closes in the same room that they are in.
When Peter gets out of Rachel's car after trying to kiss her, Rachel's body is turned in her seat and she is facing him. In the shot where Peter is walking away, she is turned and facing the windshield. When the shot returns to a close-up of her in the car, she is in the same position as when Peter was in the car with her, then she turns to face the windshield and drives away.
When Peter is talking to Chuck whilst on the surfboards out at sea, his hair isn't very wet at first, then suddenly is very wet and slicked back - just the same as when he's talking to Aldous in a similar situation later on, showing how those scenes must have been filmed at the same time.
During the scene where Peter and Rachel are talking on the cliff, Rachel's shots are shot during a sunny day, while Peter's are when it is overcast. During the shots of Rachel talking, you can see direct sunlight on Peter's left shoulder. During shots of Peter talking, the sky is overcast, and there is no direct sunlight.
(Around 57:30) When Matthew the waiter is doing his English accent when giving his demo to Aldous Snow, Aldous' shirt collar corner alternates between pointing towards his chest and away from his chest. Also the yellow beads and red beads on his necklace alternate positions between shots.
When Peter first meets Sarah and Aldous in the hotel lobby in Hawaii, Aldous approaches Sarah from behind and swats her butt with his open right hand. In the next shot he is holding his single flip-flop sandal in that same hand.
In the morning restaurant scene where the waiter brings his pineapple/rum drink and an extra rum mini (Malibu rum) the level in the glass goes from about 2/3 to about 1/3 before he picks it up to drink it.
When Peter mentions going to Laie Point and Rachel tells him it is a "Pain in the ass to get there" that is a lie. In actuality the cliff that Peter ends up hanging from is in someone's back yard at the end of Naupaka Street, 1/3 mile off of Kamehameha Hwy, 10 minutes from the resort.
In the several scenes where Peter and Brian talk over Apple's program called iChat, and the camera focuses on Peter's MacBook, the green light that should be on while the built-in camera is activated is in fact not illuminated.