Continuity mistake: When Karen arrives at work, she places her bags on the chair, and then puts them down onto the floor. In a following shot they are back on the chair, then in another shot they're gone again.
Continuity mistake: As Will collects the paper from outside the door, We see Grace sitting at the table, a pad and pen on the table in front of her. In the next shot the pen has vanished, and a newspaper has appeared next to the pad.
Continuity mistake: When the gang are at Champions on Ice, Karen gets out a bottle of champagne and a glass a starts pouring herself a drink. As the shots change, the bottle and glass keep swapping hands, even as she is still pouring.