I have used Quickshade and the much cheaper but equally effective Minwax polyshade on roughly one hundred miniatures. This pictures most definitely are not Photoshopped, but it's not quite the magic bullet as it seems.
While it certainly is a way to quickly finish a large number of models there are a few disadvantages:
1) It leaves a gloss finish on your model that, except in a few cases, is generally undesirable, which requires the application of a matt varnish to eliminate. Often times, though, you will want to protect the paint anyway, so it may or may not be an extra step.
2) It requires a bit more prep work. Mold lines on your models, along with any imperfection, become accentuated with Quickshade, but again, that's the case if you use a wash anyway.
3) It's messy. I brush the stuff on, but the technique is called "dipping" because the technique first involved dipping the entire model into the poly and then shaking/spinning it to remove the excess. In my case, after I get it on, I carefully brush off the excess, but it can easily pool in certain recesses.
It's a great way to get a large number of figures painted and ready for the tabletop quickly. A small container of Quickshade is roughly thirty US dollars, and the Minwax Polyshade (I prefer Tudor Satin), is about 8 dollars for a few pints.
Here is how I do it:
There are a ton of other tutorials and galleries on the web. Search "40k dipping"