Continuity mistake: When Joey is talking to Eddie in her dorm room, she is facing him with her hands resting firmly on his shoulders. In one close-up of Joey, her hair is hanging in front of her right ear. In the next shot of her, the hair on her right side is suddenly tucked behind her ear. Her hands haven't moved, and no-one touched her hair.
Revealing mistake: Towards the end of this episode, Joey comes back to her Dorm room and spots the envelope Eddie left for her. You can see her name written on the outside of the envelope, and it's supposed to be Eddie's handwriting. But in fact, it looks exactly like Joey's handwriting as shown throughout the series. When Joey is talking earlier to Professor Hetson and he hands her the exam booklet with her writing on the front, it's the same style of handwriting. During other episodes, we see what is supposed to be Joey's own writing (ie: her note to Dawson during the Series Finale that she leaves on his bed) which is also very similar. So in fact, what is supposed to be Eddie's handwriting on the note to Joey really looks more like Joey's handwriting, or the same person who really does the writing for Joey's character.
Revealing mistake: When Pacey and Rich are physically fighting in the office, there is a quick shot of a person who is supposed to be Pacey leaning forward over Rich and hitting him. However, if you look closely you can see that the hair on this person although dark brown, appears much longer and curlier than Pacey's current hairstyle. Also-just before that shot ends, you can see the longer hair swing away from his neck loosely on the right side. The next shot of Pacey shows his shorter haircut, so I believe the longer hair was actually a stunt man substituting for Pacey in a risky, physical scene.
Audio problem: When Jen is talking to Jack at the Helpline Office, she jokingly tells him that he is too young to be likely to "haunt them with your sad, single self." She appears to fumble her dialogue, however, and you can hear her almost switch the words around and say "single, sad self." She catches herself, and says 'sad' first instead.