Das Keyboard is one of the more unusual entries in the "upscale" keyboards market. The original concept was for a keyboard with blank keycaps. Yes, that's right, a keyboard with no markings whatsoever.
What the hell was the point of such a thing? Well, the designer thought that by depriving typists of the crutch of being able to read the keyboard, and forcing them to rely on muscle memory, it would be possible to type dramatically faster. It seems to work, as far as that goes, if you have the patience to put up with it. I've found that it's actually monumentally frustrating, but then, I'm not a traditional touch typist either.
After a few years of selling the massively expensive flat black blank version, Das Keyboard underwent a redesign, replacing its cheap and generic rubber-dome keys with mechanical keyswitches with gold-plated contacts. Also, a version with standard marked keycaps was introduced. Despite using a more expensive construction method, the price also fell, moving it from a ridiculously-priced toy (at $229) to a merely fairly expensive and much nicer-feeling device (at $70).
I decided to buy a Das Keyboard Professional, their codename for the marked-keycap version. Overall, it's rather nice. It's clicky, rather like the IBM Model M Keyboard, and feels crisp and smooth to type on. Its clicks are louder, yet less crunchy-sounding than those of the Model M, sounding rather higher in pitch. I find this makes the noise produced when typing rapidly somewhat more tinkly than machine-gun-like - opinions may vary on whether this is more or less annoying. It's rather lighter than either the Model M or its close cousin the Unicomp EnduraPro and flexes a lot more, resulting in a cheaper feel than either one. I've found it also has a fairly rare minor problem with sticking keys that result in a rapid-fire series of characters being typed.* On the plus side, it has a stylish gloss black finish and blue LEDs, plus features a two-port USB hub that comes in rather handy.
For those who like to use unusual hardware, I can say from experience that Das Keyboard works perfectly with Apple, Sun and Silicon Graphics equipment, though its USB hub is basically useless under IRIX.
All in all, I'd rate it inferior to the Model M or its newer USB clones, but rather better than most other keyboards available today, especially if you like the crisper feel that comes from mechanical keyswitches or buckling springs.
*This might be an interaction between the keyboard and my KVM. This doesn't happen when I connect my Unicomp EnduraPro to the KVM, but it also almost never happens when I use Das Keyboard Professional without the KVM. I can replicate the problem connected on its own, but I really have to be trying to.