Continuity mistake: When Grace reads Dr. Morty's letter on Karen's boat (in the last episode of season 5) it sounds at least a few paragraphs in length. During this episode, when she holds the letter up there is only a short paragraph on the bordered side of the page, and nothing on the back side.
Continuity mistake: As Leo speaks with Diane (he's on the sofa; she's in a chair) she refills her wine glass until it is nearly full. In the next shot Diane takes the last sip of wine from her glass, and the following shot shows her glass nearly full again.
Revealing mistake: In reality Deborah Messing is pregnant but her character is definitely not, so Grace has been filmed lately hiding behind big purses, pillows, counter tops, coats, etc. For some reason in this episode there was some rather sloppy shooting where Grace's waistline is concerned: When she and Karen are first entering the cabin, right after Grace says the line '...driving past 20 churches...' she turns sideways and for a few seconds there is a clear shot of her advanced pregnancy. Additionally, when Grace and Karen go to bed (also in the cabin) they have Grace lying on her back so the pregnancy is quite obvious in that scene, too.