Second, if we're willing to make people learn a different keycap arrangement, why aren't we willing to make them learn a different physical layout? I suspect a completely different physical layout would likely reduce the error rate from confusion between keycap arrangements (e.g., you'll still have to use QWERTY).
Anyone remember "Fitaly"? It was a big timesaver on my Compaq iPaq. From Wikipedia:
FITALY is a keyboard layout specifically optimized for stylus or touch-based input. The design places the most common letters closest to the centre to minimize distance travelled while entering a word. The name, FITALY, is derived from the letters occupying the second row in the layout (as QWERTY comes from the first row of standard keyboards)...
The aim of the design is to optimise text entry by organising keys to minimise key-to-key finger movement, allowing faster input through one-finger entry (compared to 10 fingers required to type efficiently on QWERTY layout). As compared to the 3-row QWERTY keyboard, FITALY has 5 rows with at most 6 letters in a row (as against 10 on QWERTY).
Keys are arranged based on individual frequencies of letters in the English language, and the probability of transitions.