Let's start with America Ferrera. America is an inverted triangle according to my book "Science of Sexy," which means her shoulders are broader than her hips. Her choice here is the right one. The gathered fabric adds weight to her hips and the one shoulder detail softens her width up top. The train also balances her and gives her a very glamorous look.
Carnie Wilson is an hourglass shape, which means she is naturally balanced and symmetrical. This outfit is a very poor choice for her body type. Hourglass shapes need to delineate the waist, something this outfit most definitely does not do. Secondly, Carnie's jacket rounds out her shoulders, which makes them appear smaller. Drawing out the shoulders and hips creates the illusion of a smaller waist, so Carnie and other hourglasses should wear dresses that define their waist. In this dress, she appears shapeless and heavier than she really is.
Julia Roberts is a triangle, which means her hips are broader than her shoulders. She is wearing a simple shift dress that does not increase her shoulder width; it actually narrows it. And this dress accentuates her hips for two reasons: it clings to her and tapers in at the knee, increasing the appearance of hips. This is the opposite of the type of outfit someone with Julia's shape should wear. However, Julia is one of the lucky ones -- with her height and weight, she can wear almost anything and still look great!
Kylie Minogue is a rectangle, which means her waist is even with her shoulders and hips. The beaded details on this very glamorous gown add weight to her hips (which is good), but it does not do anything to pronounce her shoulders. This makes her hips appear larger than her shoulders, and her body generally off balance. A better choice would have been a gown that accented the shoulders and hips evenly and defined her waist to give a more balanced silhouette.