I've been to Budapest in the recent days and had the opportunity to test some keyboards to see how usable they are regarding touch typing.
I was especially excited to try Sony VAIO laptops. Sony's laptops are very elegant and stylish, typically designed for CEOs and other high profile people. Unfortunately this doesn't mean that it's a pleasure to type on them, quite the contrary according to my experience. Flat keys look great, but they make typewriting hard because one's fingers cannot feel their position. Apple neither has a place in the market of typewriter's keyboards with their recent flat-key models. Lesson learned.
I've tried several dozen laptop and desktop keyboards, but my findings are pretty disappointing. Tactile feedback is usually poor and laptop keyboards have much more issues in general. The most frequent problem is that compact layouts usually result in inferior usability and the inventors of these shameful creations are incredibly resourceful regarding totally messing up layouts in the most non-intuitive manners one could ever imagine. I could talk for hours about this one topic alone, but I won't dwelve any deeper into this issue now.
Another interesting aspect of the Ultimate Keyboard which I've became more aware of is the keyboard technology used. Wikipedia has a fascinating page on Keyboard technology which explains most of the things that touch typists should know about the topic.
The article Mechanical Keyswitches, Membrane Keyswitches, Scissor-Switch Membrane Keyswitches is full of insights regarding the workings and efficiency of varous keyswitch technologies. I think that mechanical keyboards are probably superior to scissor-switch membrane keyboards which are superior to ordinary dome-switch keyboards. I'm not sure but I'm gonna test it myself.
There's also an interesting article about the 10 worst keyboards of all time. It's in Hungarian, but the pictures alone will scare the shit out of you.
As a last reference there's a microswitch keyboard made by a die-hard hacker named Tim Tyler who was apparently dissatisfied with other keyboards. I can easily imagine that his keyboard is superior to 99.9% of the keyboards available in the market.