So far, it's been terrific. I touch-typed on QWERTY for 10+ years (well since I was in junior high, so around age 12ish) and averaged about 85-90wpm. I switched on October 19, and switched everything to Colemak -- my phone and computer. I also switched from hitting the space bar with only my right thumb to using only my left (just for fun). For the first two weeks, I practiced 30 minutes a day by doing the lessons on learncolemak.com, and then by typing the alphabet as fast as I could a couple times. After two weeks, I was able to average 50wpm, but my accuracy wasn't too great (about 97% most of the time). A member on this board (Tony I think) said that people learning Colemak should focus on accuracy first, and that the speed would come later on. I thought the exact opposite, and wanted to get back to my QWERTY speed as quickly as possible. I started using Amphetype to track my progress, and for the next week or so, kept trying to increase my speed. However, I could still only average about 60wpm. I decided to test out the "accuracy first, speed second" method, as I decided to be more patient. My goal was 99% accuracy, no matter the speed. At first, I saw my speed drop drastically. However, now that I was thinking about each keystroke (I stopped confusing r-s, d-g, o-i), I quit making the mistakes that I normally made. About a week of this, I'm now back to averaging almost 65wpm, all the while maintaining about 99% accuracy. I wonder how long it'll take to get back to my old QWERTY speed.
You can kind of see how as I focused on accuracy (a little past the half-way point on the graphs), my speed dropped, but then gradually increased again. For anybody learning Colemak, I do suggest putting accuracy first (Tony was correct)! That way, you get into good habits early on, and most likely learn quicker.