Continuity mistake: Near the beginning of the episode, Will is pouring some wine. First, he pours a full glass and hands it to Grace, then he begins to pour another glass that obviously already has wine in it. He then hands this to Grace and takes an empty glass from her to fill, which he already filled (there is no sign that she already drank the wine in the glass).
Continuity mistake: In the episode "23" when Lorraine, Karen and Will are talking in the entrance to the church, before Stan's funeral, there is a signing book with a pen laying on it. But in one shot the pen has jumped back into the pen holder. It's back to laying on the book in the following shots.