Continuity mistake: Vivian has just taken over driving the car and its aerial is down (located on the front left of the car), in the next scene the aerial is up. After the "talking in the car" scene the aerial is still up, however in the scene after that when she turns the corner the aerial is down. (00:13:20 - 00:14:35)
Continuity mistake: The morning after Vivian's first night at the hotel, room service brings breakfast. When she's eating a croissant it cuts to a shot of Edward, and when it cuts back to Vivian she's eating a pancake which goes from being half done, to being a whole pancake again. (00:30:55)
Continuity mistake: After Vivian is hired and she jumps on the bed shouting "$3,000!" the position of the pillows changes between shots. (00:37:25)
Visible crew/equipment: After the failed shopping trip, the manager takes Vivian to his office, and lifts a chrome pot to water the plant. The film crew can be seen in the reflection on the pot. (00:42:40)
Continuity mistake: When Stuckey hits Vivian she rips his watch off. You can see it fly off to the left. When she bites him it's back on his wrist. Then when Edward pulls him off Vivian it's gone again. (01:00:20)
Continuity mistake: In the scene where Jason Alexander is talking to Richard Gere (on his early-90's cell phone), the pen on the desk in front of Alexander shifts positions between two shots, even though he's sitting with his hands away from the desk at that part of the conversation. (01:00:45)
Continuity mistake: When Vivian is standing at the elevator at the hotel after the polo match trying to leave because she is mad at Edward, the arrangement of clothes and her arms changes between shots. (01:17:45)
Continuity mistake: When Vivian is watching I Love Lucy, she goes over to Edward and undoes his tie, and then goes to get a pillow or something, in the next shot of him his tie is done again, then goes back to being undone.
Continuity mistake: During the scene where Vivian is with Edward at the hotel room, they're talking while he's inside sitting and she's outside. You can see on the first shot it's day time and when Edward stands up and goes near her it's evening time already. (or viceversa)
Continuity mistake: When Vivian is taking a bath and singing that song, the Walkman is lying on the right side of the tub, with its wires resting along the edge of the tub. When it cuts from Edward back to Vivian, the Walkman is in a different place and the headphone wire is in the water.
Continuity mistake: When Edward and Vivian first meet, and they drive off, he switches drivers. When she first gets in, she says, "Put on your seatbelt, I am taking you for a ride..." So she and Edward put on their seatbelts, but in the next shot she doesn't have it on.
Continuity mistake: When Vivian and Edward are sitting down with Mr. Morse and David for the important business meeting, they all get served ice cream in goblets. The waiters take them away, but when they stand up to leave those goblets are still there.
Continuity mistake: When Vivian and Edward are in the limo getting ready to stop at The Blue Banana so that Vivian can see her roommate, Kit, he is wearing a suit, but no vest. When he gets out of the car, a vest has magically appeared on him. Director's cut.
Continuity mistake: When Edward picks Vivian up at the hotel for their first dinner out, he walks up to the phone bank and picks up the phone with his left hand and his briefcase is in his right hand (down at his side). When he speaks with the manager, he hangs up the phone still with his left hand and then reaches up on the counter with his right hand to get his briefcase (which he never set up there). He keeps his right arm down at his side the whole time.
Continuity mistake: At the hotel, when Vivian and Edward sit in Edward's room, for the first time, she shows him a selection of different coloured condoms. The order of those condoms changes, between the shots facing her and the shots facing her back.
Continuity mistake: When Vivian, after having taken a long bath, has just been hired by Edward to stay a week, she throws herself onto the bed. The bottom of her feet are very dirty.
Continuity mistake: When Vivian and Edward are arguing, she asks for her money, so he reaches for his wallet and takes the money out. When he drops the money on the bed, part of the money is lying on the corner of his suit jacket. After Vivian walks out, when he turns to see if she took the money, it is not lying on his jacket, but at the edge of the bed.
Revealing mistake: Tire tracks from the camera vehicle can be seen in the grass in the brief shot of polo players moving toward the camera.
Continuity mistake: When Vivian is eating the croissant then the pancake, her hair is shorter and pulled behind her shoulder (I think like that) and then in the next shot her hair is longer and in front of her shoulder.
Visible crew/equipment: Early in the movie we see Edward on the phone talking to Jessica. As Edward says "goodbye Jessica" we can see the reflection of a camera crew member squat down to the floor. This can be seen near Edward's right shoulder.
Chosen answer: Posters are usually designed long after the film has been made, and by the marketing department. Decisions about the outfit may have been based solely on what was considered best by the marketing department (for instance, to match the color of the lettering in the title.) Also, Julia Roberts' head has been super-imposed onto a model's body in the poster image (just as Richard Gere's hair has been darkened). These are all creative marketing decisions.