If you wanna talk corsets, it entirely depends on what you're going for. If you want to go the "real corset" way, that is basically tightlacing (at least to me) where your "size" is two inches smaller than your actual waist size, and you are expected to tighten to that point.
Many other corsets don't necessarily do this, but they allow you to have the look of the corset, they may pull you in a bit, but they are often boned with plastic, and are of cheaper quality.
The issue with "real" corsets and tightlacing is that it can have some serious health problems. For women way back in the day when the corset was THE piece of underwear, many of them (because of prolonged use) had their organs rearranged, so that everything was either too high, or too low. Just think about that...where would you put your stomach: In your diaphragm, or down into your uterus?
I believe it took off about 5-10 years of life from the woman in question, too. That was one I heard quite a while ago, though, so don't quote me on that!
YES, corsets look amazing, and yes, I love them to bits...but please don't wear them too often, too tight, or in a way that causes you pain or a lack of ability to breathe! Corsets are difficult to fit and good ones are hard to come by...you have to dish out hundreds of dollars for good ones, and those are often boned with metal, so that it really holds it's shape. It does wonders for "the girls" and lovely things for your waist...but PLEASE consider it a temporary thing!
Unfortunately for me, because of my somewhat more extreme proportions, I have to be very careful with my corsets. I've had a few that bent so hard the bones would dig into my back, and I had red marks there for two days. Those were plastic bones, though...cheap corsets. I've never worn a "real" corset, and if I did, I'd be quite wary of anyone trying to lace me in too tight!
