Continuity mistake: When Will stops Grace, as they are about to have sex, they sit up in the bed, and he tells her he thinks they should wait. In the first shot Grace's black strap is falling off of her arm, yet in the next shot it's back up on her shoulder.
Continuity mistake: In the opening scene with Will, Grace, Jack and Karen, as they open the wine and talk about what they would like to accomplish in life, the newspaper disappears from the table during the scene, then reappears in a later shot.
Continuity mistake: When Will is sitting on the kitchen counter upset, he is eating butter biscuits from a tin, with the tin and the tins lid on the counter next to him. Then his mum comes in and they talk and at the end of the scene they hug; but now the biscuit tin lid has vanished although nobody touched it.
Continuity mistake: During the scenes with Will and Jack talking to Barry in Jack's apartment, the wine glasses, wine bottle, spoons in the salad bowl, tartlets, tray etc., change position and move about on the table between shots during their conversations.