I think the Kinesis Advantage is a very bad keyboard. Particularly, although the key switches (Cherry Browns) are fine, the way they are arranged relative to each other has very bad ergonomics, and any of the many non-Kinesis boards in which Cherry Brown key switches are arranged in a single plane has much better ergonomics. The reason the Advantage is bad is that when every key has a different "altitude" (height relative to the desk or floor) and a different orientation (the direction in which the center-line or "axis of travel" of the key points) it becomes much harder for the person to memorize the location of the keys and in particular much harder to memorize the "vector direction" (i.e., distance and direction) between every pair of keys and the vector direction in which the person's hand would need to move to strike every key perpendicularly.

I used a Kinesis Advantage (well, a Kinesis Essential, which has the same Cherry Brown switches and the same arrangement of keys into two "bowls", one for the left and and one for the right hand) as my only keyboard for about 2 years. I bought it to try to get rid of my RSI, but my RSI continued until I was shown (by a piano teacher) the Taubman technique by which piano players avoid RSI, which is when I realized that to get rid of my RSI I would have to stop typing or I would have to memorize the locations of all of the keys on the keyboard. (Actually, certain keys, like backquote, right bracket, left bracket, backslash and backspace, I do not have memorized. I look at the keyboard when using those keys.)

The Kinesis Advantage is a consequence of thinking of typing as a sort of "sign language" to be perceived and understood by the machine. That is IMHO the wrong way to think about typing. The correct way IMHO is to think of typing as a long series of physical actions. Imagine you have a plunger in front of you. I.e., a 3-inch-diameter disk of plastic attached to a beefy value or switch. Imagine that you need to activate the plunger reliably -- to minimize the chances that your first "activation attempt" will fail. So now you have some "perceptual" / "non-cognitive" decisions to make, namely, will you have to get your shoulder or elbow in a different position in order for your hand to contact the plunger cleanly and perpendicular to its axis of travel? How fast should your hand be moving when it meets the disk? Do you want to take a "backswing" before your "swing" for the plunger? (I.e., move your hand first in the direction opposite to the direction it will need to move to activate the plunger.) Good typing is more like that than it is like making signs in the air the way that users of sign language do. (The DataHand keyboard takes the typing-as-sign-language metaphor even further than the Kinesis Advantage does, and the DataHand is an even worse keyboard than the Advantage is. Here is a pic of the DataHand: http://www.atpm.com/7.05/images/dh-handinunit.jpg.)

These comments on the Kinesis Advantage can be tied with the topic at hand. The reason the Kinesis Advantage is praised by so many programmers IMHO is that those programmers do not realize or understand the need for a keyboardist to memorized the locations, etc, of all the keys. That memorization is a perceptual task rather than a "high-level cognitive" task such as planning a complicated sequence of movements or operations or solving an algebra problem. Similarly, using a pointing device is a perceptual task. (More precisely, it is much more perceptual than the alternative ways of achieving the same result using the keyboard.) In both cases, we have large vocal populations of programmers (namely, Kinesis Advantage lovers and lovers of keyboard-centric tools like Vim, Emacs and Xmonad) who prefer to substitute cognitive tasks for perceptual tasks whenever possible. I suspect that that preference is a mistake and that those programmers would be better off in the long run if they tried to reduce the fraction of time they spend in high-level cognitive tasks. A possible exception is programmers whose frontal lobes are still developing, i.e., programmers under 22 or so, but certainly any programmer over the age of, say, 25 who prefers a high-level cognitive task when a perceptual task would work just as well to achieve the goal is IMHO misusing his or her brain more likely than not. (I am almost sure it would be misuing my brain for me to do so. I am much less confident about other people although I am confident enough to use this comment to share my suspicions.) Often there is no alternative to engaging in high-level cognitive work -- it is the only way to achieve some goal -- and in that case I am all for it if the goal is important enough.

I think it is important for people expressing an opinion about a tool to state how familiar they are with the tool. Consequently, let me state that I used text-mode Emacs ("emacs -nw") every day for 18 years. When I finally switched to an editor that allowed me to position the cursor (and do other things) with the pointing device, I realized I should have made the switch much earlier. Parenthetically, the editor I switched to was graphical-mode Emacs, but I customized it to extend the range of tasks that could be done with the pointing device, and I temporarily disabled the arrow keys to train myself to use the pointing device to move the cursor. (In fact, I permanently bound up arrow and down arrow to commands that scroll about one-eighth of a screenful, which is similar to what what up arrow and down arrow do in Plan 9 and even more similar to what they do in Firefox.) Also, I would probably have switched to Textmate, Sublime Text 2 or Gedit if I had not already invested a lot of time and energy into Emacs, including the writing of 5000 lines of Emacs Lisp code to customize Emacs. I would probably use some keyboard shortcuts if where using Textmate, Sublime Text 2 or Gedit.