When Ned Fleming goes to 'his' bowling alley and starts throwing strikes, not all are technically strikes as indicated by the lane shot number light above the pins. Some strikes were actually the second shot of the bowling frame, so they'd only count as spares.
The first night at Laird's house, "Smoked California Bear" is served for dinner but later in the film Laird says that everything served is from within 500 yards of the house. While he has a lot of animals on the properly, odds are that he doesn't have any bears.
During the Christmas party, when her dad is asking Stephanie "Why Laird" there's a loose strand of hair on the left side of her face. It changes position several times as the camera angle changes back and forth.
When Ned is looking for toilet paper, Gustav tells him that Laird's house is "paperless," yet they previously served edible paper with dinner.
When Ned is trying to get into Laird's password-protected computer, the passwords he types appear as the words he is typing. For security reasons, passwords entered on a keyboard always appear on screen as a series of asterisks.
Laird tries multiple times to start a gas-powered chain saw. Ned picks up the saw and is able to start it with one pull. In reality, Laird's multiple attempts would have flooded the engine and it would need to sit for a while before it could be successfully started.
During the helicopter scene, Laird's star 'tattoos' have started to dry and crack.
During the computer hacking scenes, Kevin Dingle's family is watching Home Alone (1990). The first scene shown is one of Kevin grooming himself in front of a mirror, followed by his mother shouting "Kevin!" on the plane just before the power goes out. In the actual film, these scenes are reversed.
During the Xmas party at the end, when KISS is singing 'The First Noel', it looks like Gene Simmons doesn't really know the lyrics very well. His mouth appears to be singing different words to everyone else.
During the "hacking" scene, Ned calls Kevin Dingle who is outside his house plugging in Christmas decorations. Kevin lives in Michigan and it is December, however there is a fully bloomed rose bush covered with snow in Kevin's yard.
When the Flemings return to Michigan, they land in a United Airlines 727 aircraft. These were retired from United Airlines in 2001.
When the family returns to Detroit, the airplane shown landing is a wide-body D.C.-10, a plane that hasn't flown with United since 2001. Also, United didn't have wide-body service from LA to Detroit.
Early in the movie the car is seen turning off the freeway onto "University Avenue, Palo Alto". The freeway is shown in a rural area. However, the Hwy 101 exits to University Avenue are unmistakably urban. The exit in the movie appears to be from Hwy 280, but University Avenue does not connect to Hwy 280 - the Hwy 280 exit to Palo Alto is Page Mill Road.
When Gustav introduces intern Randy to the family, he says he graduated "summa cum laude" from MIT. MIT does not give class rankings or Latin honors to its students.