I actually found going from non-split to split surprising easy, simply because none of my old muscle memory worked anymore, and I had never touch typed up until then, so I wasn't able to go back to the old way out of frustration. A few hours of doing touch typing drills on some free online thing, and I could type at 30wpm, and then it only took about a week of doing my usual coding, IRC chatting etc to get back up to my usual 100wpm.

Also surprising was that after I got there, I could also touch type pretty easily on a normal keyboard. But my old ad hoc 5 finger typing had somehow disappeared entirely.