In reply to Peter Lancashire.

While preparing this post, I tested a "custom keyboard" that was very similar in spirit to your suggestion. I took a 7x6 grid and put the most commonly used letters (in English) in the middle: E, T, A, O, I, etc. Then spiraling out from the middle I put medium-use letters, The least-used letters (X, J, Q, Z) I put on the outside of the grid. I interspersed three space keys: one just to the right of center, one in the upper left, and one in the lower left. The idea was to reduce the distance that the cursor would have to travel to get from one letter to another. It worked! My keyboard reduced the average number of keypresses by 5, compared to the Netflix interface!

The problem, of course, is that such an "efficient" keyboard would be an aggravation to users who would constantly be asking, "Where's the R?" and " Where's the V?" Using a standard layout might be less efficient, but at least everyone knows where to look for the next letter they want to type.