Hi there!
I switched to Colemak about four months ago. I came to Colemak like this: in late summer last year, I was finally beginning to experience a tiny bit of progress with a long-standing RSI affliction, which I continue to suffer from. I desperately wanted to prolong whatever short period of time I had in front of a computer, so, without any real understanding of why it might help, I bought a Kinesis Advantage.
It turns out that a split keyboard sucks if you're not touch typing. I used not to. I tried to touch typing QWERTY very briefly, managed maybe 30 wpm on Dvorak, before typing "ls -l", thus arriving at Colemak. I was initially very disappointed with the stretch out to H, as in the HE digraph, and the occasional same-finger contortions – like the word "knowledge". I tried Workman briefly, but found it unsatisfying in other ways (I forget which), and so, I stuck with Colemak.
On Typeracer, I have a current 10-game average of 64 wpm and a peak speed of 71 wpm. I think in "casual" typing, I probably type middle 40s to low 50s. This is enough. My goal is to be able to work as a programmer again, not to be blindingly fast. (Although, of course, that would be nice.) There seems to be a fairly direct correspondence between how comfortable I can get the layout, and how many minutes I can type a day. The goal is to get more minutes, not more keystrokes per minute.
Between the Kinesis Advantage, Colemak, and a lot of remapping of non-alphabetical keys, I can some days do maybe 40 minutes without hurting myself. My particular injury (tennis and golfers elbow, both arms) is helped tremendously by 1) avoiding stretches and 2) typing softly. I'm not sure how much Colemak actually helps avoiding stretches relatively to, say, QWERTY or Workman. I think it might be better than QWERTY, and I doubt that it is substantially worse than Workman, but I have only my gut feeling to support that.
Either way, when I want to avoid stretches, I don't think changing to yet another layout would make a big difference. Most alternative layouts leave (A) special keys, like control, tab, enter, arrows, etc. in terrible positions encouraging pinky contortions and (B) special characters useful for programming in positions that require pinky contortions AND stretches for, e.g., the number row. The Kinesis helps a lot here, by having thumb keys; by allowing me to swap the shift keys with "Z" and "?"; and, I think, simply by its unique shape.
Anyway, that's my experience with Colemak. In summary, I think it has helped me more than touch typing QWERTY might have; I'm fairly certain it's better for me than Dvorak; and I'm still looking for good ways to get special keys and characters into good positions. Thanks for the layout!
