Internal organ damage only comes from the extended type of wear - 18+ hours a day over many many years. Look at tightlacing types - they're probably looking at some form of organ issues. But I tend to think of that as an extreme, and wearing a good corset for a day won't hurt.
For science though, I went ahead and put mine on, with some before and after measurements. I'm 5'10 and about 190 pounds, and without a corset I'm a fairly square 41-40-40. With my best corset on, I come in at 42-34-42; much better in my book! Granted, this brings along some sacrifices in comfort and mobility, so I only wear it for special occasions - I generally only go with a waist trainer. Also worth noting is that this is after some significant weight loss - if I tried this when I was heavier the corset wouldn't fit right, I'd have gapping at the top and bottom, and the reduction at my waist wouldn't be nearly as significant. You just can't squish a beer gut into an hourglass.
And as some people have said - expect to spend decent money for a good corset if you want results. The flimsy things you see at Victoria's Secret or Frederick of Hollywood aren't constructed well enough to give the results you'll want. Trying to use one of those will just give you lumps and will pinch, and is a lot less comfortable than wearing a proper corset. The one I have ran about $100, is made of a heavy brocade, has a full stainless steel busk, and 22 steel bones in it.
