Summer decides to stay at Marissa's house while Marissa meets Ryan for lunch. Summer gets Seth to help her remodel Marissa's room as a surprise. Later on when the room is supposed to be in the process of being remodeled Marissa and Ryan are hanging out downstairs at Marissa's house. They were supposed to be at the diner having lunch.
When Seth and Summer are remodeling Marissa's room Seth is trying to hammer a nail into the wall. He hits the wall too hard, missing the nail, and the nail remains in the wall closer to the top-right corner of the hole. In the next shot, the nail is is now closer to the top-left corner of the hole.
When Luke is drunk, talking to Ryan on the phone, he is standing outside his truck with a beer and listening to music. The shot goes to Ryan and then back to Luke hanging up on him and the music is no longer playing.
Marissa's old yearbook says "2002" on the front. But she is a sophomore in 2004, so it should have read "2003" at the earliest.
After Seth is crying, he suggests to Summer that they will be watching football the next day. Summer says that football season isn't for another 5 months. This indicates that it is around March or April during this scene. After the opening credits, Seth says that he is going to go watch hockey. Ryan says that the hockey season is over, however, if it was March or April hockey season would not have been over because it ends in the middle of June.