Let's take a look at some of the red carpet looks that featured boobs.
Shiri Appleby and Julia Louis-Dreyfus wore gowns that were nice examples of a trend that I would describe as "banded deep decollete". This category of gown features a plunging neckline that is held together with one or more bands of fabric wrapping around the wearer's rib cage. This allows the V-neck to be extremely wide without requiring the use of double-sided tape. Appleby's long, straight column was a flattering style on her slim figure, and the color was gorgeous on her. Louis-Dreyfus' narrower neckline with criss-cross straps and a fuller illusion overlay was lovely and flattering on her, as well.
Angela Bassett, Tina Fey, and Allison Janney were perfect examples of how (forgive me) older actresses can make the revealing neckline work well for them. Bassett's canary yellow gown was something of a stylized kimono, with wide, flared sleeves, a broad v-neck, and a slightly flared skirt with a small train. I didn't love the color on her, and the overall style was somewhat bland, but the neckline was controlled and flattering and didn't show too much skin, so I'll give her look a hesitant thumbs up.
Fey's green Grecian gown was gorgeous. Its full but soft skirt flared out from a wide crushed sash high on her rib cage which allowed for a deep v-neck that was firmly anchored in place and looked deeper than it actually was. She looked comfortable and was able to move without fear of a wardrobe malfunction. This is what all revealing gowns should aim for.
Janney's gown had a broad v-neck that showed more skin but less cleavage - a very nice illusion for ladies of a certain age who may not have quite as perky a figure as they used to. Janney's gown pairs the revealing bodice with a slim, fitted skirt with a high slit and a small train, perfect for showing off her toned legs.
Kristen Bell and Jessie Graff wore gowns with bodices in another popular style, one that I describe as "wide suspenders". It's pretty much two bands of fabric that go over the shoulders and tuck into the waistband. They don't actually meet at the bottom, so it can't be described as a "v-neck". There is usually much double-sided tape required for this look, and it is definitely more flattering on less buxom figures (which Bell and Graff both have). I loved the patterned fabric in Bell's dress, although the skirt of the full ballgown was so voluminous that it looked out of proportion with the minimal bodice. A bit less fullness and this would have been a very nice look. Graff's wide, high sash and gathered fabric allowed her a little more firmness (and a little less double-sided tape), and her softly gathered gown with a deep slit was nicely proportioned and graceful.
Laverne Cox and Claire Danes both wore gold lame concoctions which nicely illustrate how similar gowns can look different on different figures. Cox's curvy figure defied gravity in her clingy v-neck gown, emphasizing both her height and her voluptuous figure. Danes, on the other hand, has a much more slight, straight figure, which was not quite as flattered by her "starburst" bodice, but which worked well with her full skirt and wrapped sash. Point to Cox.
Portia Doubleday opted for a mostly full-coverage column with long sleeves and a high boat neckline, but which featured a large triangular opening in the front allowing just a peep of side/underboob. It was...interesting. I didn't hate it, but I didn't love it, either. The color was spectacular for her, and the simplicity of it, with just a few details like the folded pleat at the waist and the slightly overlapped neckline, gave it just enough visual interest. Rhea Seehorn's gown used a similar triangular cutout, but worked into a shoulder-revealing halter top accented by a black neck strap and tiny black belt. The more fitted bodice of Seehorn's gown wrapped her figure nicely and held the fabric firmly in place, which I found a more attractive look than Doubleday's.
Kirsten Dunst and Sarah Paulson both wore gowns with necklines which, in my opinion, showed more skin than was truly flattering. Dunst wore a plunging, broadly v-necked gown which featured plenty of cleavage. Instead of a straight "V", the neckline was arched outwards, allowing for even more visible skin. Unfortunately, that gave me the impression of the fabric being strained and poorly fitted. It was a shame, because the rest of the gown was stunning, with its see-through skirt with vertical lines and zig-zag-edged bodice, and perfectly tailored to skim her figure without being tight. And the pure black was perfect for her icy blond coloring. The devil really is in the details.
Paulson's gown was something of a hot mess all over. The deep v (which ended at an odd level near her navel) emphasized the straightness of her figure, especially with the very square shoulders, the 3/4-length sleeves, and the straight skirt with only a tiny back train. A bit of softness or curves was needed somewhere. And the long metal fringes which swung and dangled as she moved made her look like an unfortunate Christmas tree. Great color, terrible dress.
Judith Light, Abigail Spencer, and Constance Wu all opted for a bit of illusion, wearing narrow but plunging necklines with modesty panels (see-through or flesh-toned fabric which creates the illusion of exposed skin) holding them firmly in place. The geometric art deco lines of Light's silver and white gown emphasize her slender figure, while Spencer's fuller, flowing midnight blue gown created younger, softer, and more feminine lines, adding a few curves to her rather straight figure. Wu's cobalt and black gown was all smooth, graceful curves flowing beautifully to the floor with a tiny all-around train. Three very different but very effective and flattering looks.
And just to prove that not everyone opted to flash their boobs, here's Anna Chlumsky showing that modesty doesn't always equal good fashion.