Continuity mistake: When Andy and Miranda are in the limo in Paris, they pull up to the curb and there is a bunch of press waiting as Miranda opens the door. However, when the shot changes, it is not the same group of people - in particular, there is a balding photographer who should be standing right there but is nowhere to be seen. It all happens too quickly for that much change.
Continuity mistake: This one has to be watched carefully but can be seen without slow motion - when Emily hits the taxi's windshield, the front shot shows her hit the hood with an orange package under her - it looks more like a box than a bag - and her purse in her right hand. Before she was hit she also had a small orange bag in her hand. A shot later, the side view of the accident shows 3 orange bags flying through the air, and her purse is on her left arm, not on the right as it should be.
Continuity mistake: When Nigel is toasting himself about what he thinks will be his new job, the glass is in his hand. The next shot shows his hands are empty and he grabs his head with both hands and walks to the window. Andy then brings him the glass. The glass is in his hands and the very next shot (no time lapse) shows the glass on the counter and then next (no time lapse) in her hands.
Continuity mistake: When Andy meets her friends in the restaurant, Lily is holding a french fry which goes from short to longer, from straight to crooked, over the course of three or four shots.
Continuity mistake: When Miranda tells Andie that she wants the Harry Potter book, Andie goes back to her desk and her Sidekick is on her desk. She had put her purse down but not her phone because she never got a chance to pull it out.
Continuity mistake: In the restaurant where Andy is giving her friends presents, she hands her friend a little clear case of Clinique products, but when she's putting them in her friend's hand, she is also holding a blue box when she wasn't before.
Continuity mistake: Emily has a bad cold/flu the day of the benefit Miranda hosts - her nose is extremely red and she's congested. Miranda tells her Andy will have to go too, so Emily shows Andy photos of clients to memorize; suddenly she has no sign of a cold at all - the redness just disappears, which wouldn't happen that quickly. That night it's back in full force, just as it was earlier in the day.
Continuity mistake: Not only does Andy not have the bagel when she enters the subway stairs, but she is wearing her gloves/mittens when she does - when the bagel reappears, they are gone.
Factual error: The first time Miranda Priestly arrives in the office, everyone scrambles to make themselves look better. One girl uses her webcam to apply makeup, but the image shown in the computer monitor is as though the monitor is a mirror. Given that she is looking directly at the screen rather than at the webcam itself, her eyes should not be shown looking directly into the monitor, but rather just below (if it is a top-mounted webcam).