Continuity mistake: When Jack is talking to Will at the kitchen area, as Will says "I'm fine, I guess I was just scared", in the first shot he is shaking a bottle of salad dressing. In the very next shot he is now instantly mixing the salad with a pair of mixing spoons.
Continuity mistake: Near the start when Will, Grace and Jack are talking about the new swimming pool, Will starts to peel an orange. In the first shot he peels some of the skin off and drops it on the table. In the next shot there is no peel on the table and he is still peeling it. As the scene goes on, the pile of orange peel on the table that he leaves, keeps changing position.