Continuity mistake: Season 5, episode 1, "The Larry David Sandwich." After Larry's near-death experience, he's at a party talking to Jeff and drinking from a very small cup. At first Larry's fingers are in the handle, but when he actually starts complaining about how small the handle is his entire hand is cupped around the cup.
Plot hole: In the final episode of season 6, Larry tries to find the name and phone number of the woman he was talking to in the waiting room. The receptionist begins to list the names on the sign-in sheet until she reaches 'Paula'. Larry nods to this, however Paula never told him is name, nor was there ever an off-screen moment when she could have. She could have been any of the women the receptionist named.