I just switched from a Matias Ergo Pro to an Ultimate Hacking Keyboard. It was a pretty big change - not only did the mechanics change (browns vs alps, 6 on the left, no escape/function row, solid palmrest instead of squishy), but I swapped control and caps lock, and configured a bunch of stuff with layers. It has been 2 months and I'm almost there.
The weird thing is that just because I learn to use the new control position for ctrl-c does not mean that I have learned the new control position for ctrl-a. And even weirder, just because I learned the new control position for ctrl-a for select all does not mean I learned the new control position for ctrl-a as a GNU Screen shortcut. My mental mappings are based on what I am trying to do, not what keys I am pressing.
I also switched from ANSI to ISO, and use the left |\ key as shift and the left shift to activate the mouse layer. Usually it isn't a problem, but when I move my right hand far to the right (e.g. to hit the right |\, I tend to move my left pinky farther to the left to hit shift. My wrists like to make symmetrical movements.