Amar Sagoo has posted a fantastic summary of 1997's Handbook of Human-Computer Interaction... specifically its sections on optimal keyboard design. Sagoo supplements this with many of his own observations. It's a fascinating dissection of the qualities that contribute to the perfect keyboard, jettisoning vague complaints about keyboard "smooshiness" in favor of highly objective haptic terminology like "clickiness:'
One of the most-cited criteria for keyboard aficionados to prefer a certain keyboard over another is “clickiness”. The idea behind this is that a good keyboard should give you some tactile feedback when you've successfully “actuated” a key, and that you shouldn't have to depress the key all the way to the bottom to be sure, as this would not allow you to type very fast. Some keyboards don't click at all, some give a softer and others a sharper click. The exact behaviour can be described by a graph plotting how the physical force required to push the key varies along its way down and its way up. The sudden dip in force on the downstroke is where you will feel the “click”.
Read the whole thing, it'll solidify your thoughts about your favorite keyboards.
Science of Keyboard Design [Amar Sagoo] (Thanks, Joel!)