Hi to everyone. I'm new here and in the process of reading up. Couldn't resist responding to a corset thread, though.
I have a little experience with corsets, and if you're in the US, then Versatile Fashions is a great place to buy from. Dark Garden and Stormy Leather are both excellent corset makers, too.
I've had several corsets from Versatile over the years, and always been happy with them. They're very well made and durable. I've never bought from Dark Garden or Stormy Leather, but they have great designs and I've only ever heard positive comments about them.
As for some of the questions posted, I've collected answers to most of them over the years--
The modification of the lower ribs (the floating ribs) by a corset is possible, but requires pretty dedicated corset training (think about moving teeth with orthodontics-- you have to have braces for years sometimes). Someone had mentioned 20 hours a day and that's pretty close to what you'd need.
The same goes with waist slimming. There's quite a bit of dedication required, but the shape a corset gives is just amazing.
There are a few things to keep in mind, too.
First, new corsets require a bit of a breaking in period, so that the boning can adjust to your body. Cinching a corset closed when it's brand new can stress the bones and damage the corset. Plus, you have to let your body adjust to it. In most cases, if you've never corsetted before, you might only be able to wear it for an hour or two at a time.
Also, you want to get a corset with a metal busk and steel stays. There are a few different types of steel that can be used, and if I remember correctly, the spiral steel is the strongest. Avoid corselettes if your goal is waist training/tightlacing. Corselettes aren't made to deal with the stress of tightlacing and will break/rip/tear easily because they aren't reinforced the way a good corset is.
A corselette is good for a waist reduction of about 2 inches from your current waist size. A good corset should be able to reduce your waist anywhere from 2 to 4 inches. Individuals who have been tightlacing for a while should be able to get as much as 6 inches off their waist.
Last--A corset is not a good way to get into clothes that don't fit. The bulk of the corset will add width to your torso and depending on the corset, to your hips, too. Some jeans, etc. might not fit the same as a result.