I've been using colemak for a couple months now. I'm still not up to my qwerty speed, but am already fast enough that it isn't a burden, and I am liking it so far. It's actually pretty hard to give an objective opinion on it. I do notice when I need to type on qwerty that I have to move my hands a lot more to be efficient, where in colemak I can leave them on the home row for the most part.
I have tried to learn dvorak a couple of times in the past, but always failed, because I couldn't really tolerate the speed drop of going back to hunt and peck while I learned the new layout. (When you're trying to do your job on a computer, 5-10wpm is insufficient.)
Anyone who wants to learn colemak, forget trying to go 100%, and check out tarmak. It's a set of 4 transitional layouts for switching from qwerty to colemak. Each one moves 3-4 keys, so you can learn it a bit at a time. Because only about half of the keys change, it can be done without much overhead in relearning. The only key that gets moved around repeatedly is the j.
Because it's only 3-4 keys out of place, it's not too much of a penalty to your typing speed. You need to think about where those keys are, which will slow you down, but you should still be able to maintain a usable speed. once you get back up to say 40wpm, you move onto tarmak2, where another few keys get scrambled, and so on.
It was around 10 days before I was switched fully to colemak (the first couple steps went very quickly) but I maintained a usable typing speed throughout. If I hadn't used tarmak, I might have gotten to the same point a couple days sooner, but I wouldn't have been able to work normally in the mean time.
