When the druggies are in Grace's office, one of them knocks over her purse with his foot. In the next shot the purse is standing straight up again.
The position of the red booster seat which the Cher doll sits on changes between shots.
When Will, Grace and Jack are having the birthday dinner in the restaurant, in one shot Will picks up his wine glass and commences to drink, yet in the very next shot the wine glass is down on the table.