When Maggie takes a Polaroid picture of Jamie in the parking lot, Jamie raises his hands to block the shot AFTER the camera flashes and we hear the motor crank out the picture, meaning the camera had already taken the picture. Later when we actually see the picture, the picture has him with his hands raised.
When Jaime and Maggie are eating cereal on the couch and Jaime is telling her the story about his report card, he is eating out of a box of "corn flakes", but he is eating cheerios out of his hand. Likewise, Maggie is eating cheerios out of her bowl.
When Jamie is leaving Maggie's apartment the buttons on his white shirt alternate from half-buttoned to fully-buttoned each time we see him.
When Jaime is on the couch eating cereal at Maggie's house, the box reads "corn flakes". The label switches from facing the camera to facing away from the camera. Also, the box switches from the corn flake box to what appears to be a Honey Nut Cheerios box.
In the car when Jamie is being transported to the hospital, at some points when Josh is talking to him it cuts between different shots of Jamie looking out the window or looking straight ahead or at Josh, when there isn't enough time for him to move his head between these shots.
Near the end, a video is watched from a Fisher Price PXL 2000 camcorder hooked up to the TV. Audio is heard but only the yellow video cable is connected. These camcorders had an RF modulated output so video and audio were output through a single cable and modulated so a television could tune into the signal on channel 3 or 4 when attached to the antenna connector.
When Maggie is using the camcorder in bed to videotape Jamie the camcorder is tilted, but the black-and-white shots of of Jamie are not.
When Maggie falls to the floor after walking in on Jamie and his brother, her "modesty patch" is clearly visible.
When Jamie is looking up something on the iMac computer, he is using an "Apple Pro Mouse", an optical mouse that was introduced in the summer of 2000. The movie is set in 1998 when Viagra was first introduced by Pfizer.
Xanax is listed as a drug made by Pfizer. This wasn't true until after Pfizer merged with Pharmacia (formerly Pharmacia & Upjohn) in 2002.
When Maggie gives Jamie Pop Tarts, the box is historically correct, but the foil wrapper is the style that is used currently.
When Jamie is presenting TV-Sets in the opening scene, he introduces three 52-inch Flatscreen (or bigger) models by Philips, Samsung and Magnavox. The scene is set in 1996. 1997, Philips introduced the first 42-inch plasma display (US $14,999) to the retail public in 4 Sears locations in the US. 52-inch displays weren't among their Flat-TV range until at least 2003.
Jamie and Maggie are in Chicago. In the scene where they walk across the street after the unConvention, the street sign clearly shows "Seventh Avenue." There is no Seventh Avenue in Chicago.