For several years I've been trying to learn touch-typing, but failed one way or another. Most probably by not having willpower strong enough to stop looking at key labels and actually try to learn the positions by heart. At some point, I started working as a programmer, still doing the old bad hunt-and-peck.
I took my chance with Colemak during a two week holiday, in the `all-or-nothing' way. I.E., both new layout, and *only* touchtyping. I did *not* rearrange the keys, neither re-labeled them, but left them mis-matched with the layout; I wanted to learn it all by heart from the beginning. It took a lot of self-discipline, allright, but having the key labels not match current layout seems to help there.
At first a major drag, but, step by step, I started to memorize positions of keys. `KTouch' tool from KDE was very helpful. Also, very helpful were code autocompletion facilities in IDE and text editor I'm using ;) At first, I also kept a picture with layout on the screen, but that was just interminiet phase.
When I got back to work after those two weeks, I was still somewhat slower than the previous hunt-and-peck, but I clearly was improving. After a month or so of daily use, I became comfortable with the layout, and achieved the holy grail of typing, the touch-typing.
The backspace on the left of alphabetic keys is instant win, feels very natural after just a bit of use.
As my native language is polish, I made one important change to the layout, by setting <a>, <e>, <o>, <s> <l>, <z>, <x>, <c> and <n> to produce polish accented characters with <alt_gr>, as it's default with QWERTY. Clearly, that's a big departure from Colemak's way of character composition, but it works for me and is reasonably fast. I barely ever compose any other non-ascii characters.
One feature I miss from Colemak as compared to QWERTY is that the <`> / <~> key does not compose to <¬> (logical negation) character, which I like to use at times for emoticons. Probably I'll deal with it at some point ;)
As for occasional use of QWERTY on computers where I can't set up layout, well, not much of a problem. Slow? Sure, but not slower than I was doing before. Embarrassing? Maybe a bit, but certainly not a big problem.