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. (00:59:20)
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. (00:47:30)
Continuity mistake: After Grace pours Jack some eggnog, we see the pitcher on the desk, and no eggnog is visible. It then shows Karen getting out her laptop, then back to a shot of Grace looking stunned, and now the level of eggnog in the pitcher has almost doubled. (00:01:25)
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. (00:17:00)
Continuity mistake: When Grace and Karen enter the cabin, Grace puts her bag down on top of the sofa, so that the large bottom faces the door. In the next shot when she walks back over the bag has now changed position so that the bottom of the bag faces us. (00:04:50)
Plot hole: In the bowling alley scene, Ellen states that Grace would need to knock down 27 pins in order to tie. Will and Grace then have a conversation, and Grace gets a strike with her next ball. They then start gloating that they have beaten Rob and Ellen, but the scores don't add up, and they couldn't go into the lead on that round.