I've been typing with Colemak now for about 10 months. My speed has dramatically increased over my querty skills and it feels so much better - might sound strange to newbies but it feels a lot "rounder" to type in colemak.
The first 2 months were hard, I practiced a lot in the evenings because I had to get real work done during the day and couldn't "play" with the new layout.
I have to work with remote desktops at work so I often have to switch back to querty. I got used to looking at the keyboard once in a while for querty typing and looking at the screen for colemak typing. It works really well for me and I can switch back and forth easier than I had expected. querty speed is a bit slower than before.
For passwords that I frequently have to type in querty and colemak I only use the common keys - works well.
CTRL+Z,X,C,V is the killer argument for using colemak over dvorak. CTRL+Y for redo was the hardest one for me to get used to in colemak - not sure why.
Bottom line - after two months and completely switching to colemak it was fun. Will never go back to querty - hope that the layout will be shipped with every OS soon so that kids can learn the better way of typing from the start.
If you can make it through the first two months you will be rewarded!