Update at 2 years.
Now that I have been using colemak as my dedicated layout at work and home for just over two years, my typing speed has been around 60 wpm as measured by typeracer.com average for some time. I'm completely happy with the layout, and also with my speed now. If I wanted to improve my speed now, it would require a lot of time to practice.
As a side note - The kinesis keyboard is really great. And for anyone that does a lot of typing I would also suggest switching to a keyboard with mechanical keys to make typing much easier on your fingers.
hi-games profile - http://hi-games.net/profile/5186