When Miranda calls Andy in Paris, Andy looks at her T-mobile sidekick and it's ringing. The phone shows Miranda's name and under it, it says, "Connecting." For it to say that, Andy would have had to call Miranda and her phone wouldn't have been ringing.
As Andy is distributing Miranda's unwanted items, Miranda calls; once Andy gets the phone from the others, she is talking on the Sidekick upside down. You can clearly see the multi-directional pad which is the earpiece.
When Emily is sick Miranda calls it "an incubus of viral plague" an incubus is not a breeding ground or carrier of germs. It is, in general language, a burden. It had been an evil spirit who visited women at night to have intercourse or nightmare.
When Nigel and Andy are toasting for Nigel's new job, they're each holding a glass. In the next scene Nigel has no glass but Andy is still holding hers, then the camera shifts and Andy is holding both glasses.
When Andy is telling her friends about getting her new job while at Nate's restaurant, Nate pours wine five times on screen when there is only four of them at the table and actually only three of them are drinking.
When Nigel offers a pair of size 8.5 sling-back pumps to Andy on her first day at the office, Andy sets them on her desk before Miranda calls her in. When Andy sets them down the points face toward her seat at the desk. In the next shot where she is running into Miranda's office, the shoes now point the opposite way where Nigel is standing.
When Miranda and Andy are being driven in Paris after the luncheon, they appear to be circling Place de la Concorde based on the view out the window. You can see Pont Alexandre III several times and other landmarks around the Place.
When Andy Sachs is talking to Nigel outside New York and photographing the "Urban Jungle" shoot, at the end of their talk Andy pushes her hair behind her ears with one thin strand in front of her ear. The next time you see her, a second later, all her hair is over her ears.
When Miranda is telling Andy about her lumpy blue sweater, the blue belt on the ballerina dress changes positions. First it is with the buckle over lapping the belt. Then in the next frame the buckle is behind the belt.
At the office preparing for the fashion party Emily has a terrible cold and her nose is bright red. When they arrive at the party (getting out of limo) her nose is normal. Inside the party while greeting guests her nose is once again red.
When Andy arrives at work, on the day Emily and Miranda see her makeover for the first time, when she is seen holding the door for someone pushing a rack full of clothes through the doorway the purse she has hanging on her shoulder is made of brown leather and has a long strap with a large tassel hanging on it. Later in the same day at James Holt's party, when she was picking up the sketch of Miranda's dress, her clothes and jewelry are the same but she's carrying a completely different purse.
When Emily is pulling faces listening to Andy going on about how her father is visiting town and might take her to see "Chicago", the same pair of extras walk in the corridor behind her, twice within seconds and each time from left to right.
In the first part of the movie, Andy buys a bagel from the bakery. When she is crossing the street, there is no sign of the bagel. But in the next shot of her going down the stairs, she's eating the bagel again.
When Miranda is telling Andy that she is getting divorced, Andy's sitting position keeps changing. One moment the camera is on her and she is sitting with her legs crossed, the next they are uncrossed.
At 39:41 of the film, Andy is seen entering the Spring Street 6 train (subway) uptown on a train that says downtown only. Immediately after this in the same sequence she is exiting the 51 Street 6 train downtown stop. This would have been impossible on two fronts, since she would not be able to get uptown from Spring Street to 51st on a downtown train and furthermore surely would not have exited at the downtown stop at 51st street if coming from Spring.
At the end of the movie when Andy sees Miranda coming out of the building and getting into her car, Andy is walking on 49th street, traveling east from 7th avenue toward 6th avenue. In the next shot she is walking south on 6th avenue, crossing 50th street (Radio City Music Hall on the corner). She would have had to walk east on 49th street to 6th avenue, walk north on 6th avenue beyond 50th street and then turn around and walk back south.
The goof item below may give away important plot points.
At the end of the movie when Miranda pretends not to see or ignore Andy who is walking on the other side of the street Miranda is riding in the back of a Mercedes. No one is in the back seat when we see a wide shot of the car pulling away from the curb.