When Kate stops Charlie while they are making out on the bed, he says "Maybe I was afraid of getting married." When Kate responds with "Charlie, You weren't afraid of getting married to her", her lips aren't moving until the last three words of the sentence.
When Kate first met Bob (the "Eurotrash in an Armani suit" thief) at the George V Hotel, he spoke perfect English. When she met him again at his apartment when Luc was helping her get her things back, it seemed as if he spoke no English. Luc was used as a translator during the entire scene.
When Kate finally gets Charlie back and they are in the hotel room fooling around, Kate pulls away from Charlie and her hair in the back is sticking straight up. In subsequent shots, her hair repeatedly switches from messy to perfectly done and back.
In the scene where Kate confronts Charlie on the beach, the sunlight begins on Charlie and Juliet's left sides, but as soon as she is offered a seat, the light switches so that it's coming from behind Kate and shining on their front/right sides.
At Luc's room when he was showing Kate his childhood's project with wine, he forgot to ask her to close her eyes before she tastes the wine for the second time. finally he did but he was late because she was already drinking.
When Luc and Kate are taking of from YYZ (Toronto Pearson airport) on their way to Paris, we see outside the windows vast expanses of farm or forest land just at the end of the runway. There are only mass urban spaces, ie: buildings and major roads at the end of any of the runways at YYZ. Also, while the aircraft is taxing to the runway we see structures at the airport that do not exist at YYZ.