I started touch typing with Colemak around the beginning of spring and practiced every day for the first 8 weeks -- but only sporadically after that. The point at which I really switched over was about 30wpm, although I didn't feel comfortable until I could sustain 40-45wpm.
Before Colemak I was only a 4-finger typist; I did not touch type at all and my average speed on Qwerty was about 50wpm. Now I'm at that speed with Colemak touch typing, and have been for a couple months. My accuracy is about 94% for actual text, and about 97% in Amphetype. Getting to 60wpm would be nice, so I plan to resume practice to get to that speed.
As you can imagine, learning touch typing was very hard esp. when you come from 50wpm speed on Qwerty and with no touch typing experience. Barring language barriers, it seems like the worst of all worlds. Someone with no typing experience would probably suffer less frustration than I did because they have no history or expectation of being able to just sit down and do 50wpm.
The two factors that were at least of some comfort were my pristine and new (to me) Dell AT-101W Alps board, and of course Colemak itself. With the drastically reduced hand and finger movement, I knew by the time I reached 12wpm that I wanted to stick with Colemak (and I'm so glad I did)!
If I could point to any mistake that held me back, it would be starting Colemak (or any layout) without the intention to stay relaxed and accurate. Forcing yourself and correcting too much won't allow you the mental breathing space to develop helpful techniques.
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P.S.
I do find it a bit perplexing when people suggest that Colemak causes 'compatibility' problems because it is too different from Qwerty, and then suggest an alternative layout that changes slightly less keys. Any time you wish to stick with any alternative layout there is some potential for disappointment. Personally, I do not find it a challenge to momentarily switch to Qwerty when I'm in a situation were I can't use Colemak (it may be easier for me than others, because Qwerty is entirely different for me with look-hunt-and-peck).
If you think you *might* like Colemak, then give it a try anyway and see if you can get up to 20wpm and see how you feel after 4-5 weeks.
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P.P.S.
I did look into some of the other alternatives like CarpalX, Workman and Dvorak before deciding to try Colemak. None of them seemed to offer a clear advantage over Colemak, and though I occasionally considered Dvorak over decades I guess it never pulled me in because the analysis behind it and the results were too feeble for it to really shine. And despite Microsoft being asleep as usual, having built-in support in Ubuntu and OS X really matters so Colemak it is. If I ever try another layout, it will be something more radical like Arensito; IMHO we've gotten about all we're ever going to get from the current set of assumptions about key placement and modifiers.