Hi. I'll comment my experience after some practice with colemark.
I 'm using QWERTY since I had a computer, I didn't learn to touch type properly, and I had a speed of about 50 WPM in QWERTY (I measure it with keybr.com ).
Some months ago I learned about alternative layouts. The idea made sense to me, specially after reading the statistics and reasons for something better than qwerty. So first I tried Dvorak. I couldn't get used to dvorak, I couldn't gain speed easily, found hand alternation awkward and made many mistakes with the Ctrl+Z, X, C and other shortcuts.
Then I read about Colemak and I tried it. I like the change of the Caps lock for Backspace, I have no problem with shortcuts with Colemak, and I found it much easier than Dvorak to learn. I have been practicing Colemak about 10 minutes a day for the last 3 months, and right now my speed is 36 wpm. i'm finding it hard to improve speed now, but I guess I just need more practice.
I often have problems with the "R" in Colemak, it's the letter with which I make more mistakes. I believe it's only a matter of practice.
To practice typing, I'm finding useful the following program https://code.google.com/p/amphetype/ because it can use any text I like to practice. It's meant to be used when you already learned the layout. To learn the layout I used mainly keybr.com
I would recommend Colemark to anyone wanting to learn to touch type. It certainly is more efficient than qwerty regarding finger movement and also the transition from qwerty seems easier than in other layouts.
I still use mainly qwerty because I often share my pc and I'm still faster in qwerty, but I'm willing to fully switch to colemak once my speed increases.