Having watched the segment on soft proofing on the "From Camera To Print' Videos from Luminous Landscape and having read the questions generated on their discussion groups, it appears that a lot of people still don't GET soft proofing.
Many months ago I had to ask some repeated and blunt questions with followups to get the experts to explain the real story to me so let me add the following explanation to what Jeff and Michael presented on their talk.
A printer profile does two things. First it attempts to adjust the printer output to match the computer file as closely as possible. It can't match it perfectly - pigment and dye inks are not the same as monitors, either in colour or in dynamic range. There are limitations to how close the printer can get. If the computer file includes an intense orange but no combination of printer inks can print that intense an orange, then the printer profile isn't going to make for a perfect match.
When profiles are made, the difference between where the printer got to and what the computer wanted is noted along with the instructions for getting as close as possible. it's like catching a bus to a friend's house. It can take you most of the way there, but it can't usually deliver you to the door. In the case of the printer profile, it does at least provide you with a map from the bus stop to your friend's house so you know what direction to walk.
It's this business from best possible to ideal that most people don't even know about in printer profiles, and this is the part that makes soft proofing work.
By using the printer profile, the soft proofing knows that no matter how you try, there is only so much orangeness in the inks to represent the carrot picture. The soft proof shows you this difference by toning down the orange of the original computer file to the maximum the inks are capable of. As you can toggle soft proof on and off quickly you can get a sense of what's missing.
You then have the option of adjusting the original computer file to compensate for the deficiencies in the printer. For example, if you can't get the printer to make the orange that intense, perhaps you can increase the grayscale contrast to make the carrot look more snappy. Maybe you can add a bit more red to compensate for the orange deficiency.
Every printer and every set of inks has these deficiencies. Mostly we can live with them, but sometimes we need to work round them, and soft proofing is the tool that helps you do that.
The other problem with the print is that the dynamic range from brightest paper white to blackest black is going to be a lot less than you can get on any computer screen. If you turn on paper white in the soft proofing, the computer attempts to emulate the narrower dynamic range of your print. If you are using glossy paper with it's increased dynamic range, the differences aren't all that huge, but the blacks are more of a muddy gray. With matte papers though, the soft proofed images tend to look terrible, very flat and dull. it turns out they are accurate, it's just that we get so used to the full range of brightness on the computer screen, and of course you can still see full white and full black surrounding the soft proofed image on screen. If there were no other part of the screen showing at all (ie. the image filled the screen to the edges in all directions), you would be more able to buy in to this flatter looking image. Jeff mentions in the video removing as much of the screen clutter as possible but the problem with the black surround is it makes the dark areas of the print look pathetic. I suspect a gray background would actually work better.
I find that it is more useful to look at the detail in the shadows in the soft proofed image rather than the absolute darkness of the blacks and use that to adjust the shadows as needed to better show shadow detail. If there is lots of detail in the soft proofed shadows, then it will be readily apparent in you print too. If it isn't, then there's a good chance that no matter how deep the blacks are in your print, the shadow detail isn't going to be great.