Hey! I figured since I've been using the layout and love it I should share my thoughts and experiences, I mean, some on these forums made or broke my experience at times, maybe mine will to someone else :)
Anywho, I'm 18, been typing on qwerty for probably 10+ years. I don't touch type perfectly (I mess up with the number row) I do mostly type properly and have taken courses in typing. My WPM has been roughly anywhere from 70-100 depending on what I'm typing and how relaxed/focused I am.
I switched to Colemak maybe 3-4 weeks ago. I've wanted to switch for probably a few months but tried to go "cold turkey" but it ahh...didn't go very well (lol). I'd want to find things to practice typing with but then when I actually want to use a web browser, IM or IRC client I'd get frustrated at my lack of speed and switch back to qwerty. My current Colemak WPM is maybe 30 WPM and growing, for the most part my fingers only really get confused about the top row (f, p, l, and y keys are my problem) so once I get past those personal hurdles I'll be doing much better.
I currently use GNU/Linux, Arch Linux at the moment, though I'm still a fan of Debian, Ubuntu, and Fedora. Something that helped me with switching was using bash aliases for qwerty and Colemak. The alias "colemak" (alias colemak='setxkbmap us -variant colemak') switches to Colemak for me, and "qwerty (alias qwerty='setxkbmap us') sends me back to qwerty (Note: this only works when running X11, in just the tty it won't do the trick).
My most important tip/advice would be directly from one of the pages on the site that says "Don't change your keycaps!".
Seriously, don't.
It just slows down your brain and muscle memory from developing, and it really hindered me and stopped me from committing the first time or two I tried to switch.
The feeling you get from typing with Colemak (especially if you type fast/correctly in qwerty ) is amazing, it's hard to describe. It's mostly the feeling of moving your hands much less and more comfortably, once you start to get some speed with Colemak and type with qwerty it really stands out.
Also, a note for Vim/Emacs fans/users, it will mess up your muscle memory. Especially with Vim and the hjkl keys for navigation. However, I wouldn't recommend using Colemak.vim or remapping any keys, navigation, while strange at first, will become second nature. Don't bother messing up the bindings for simple commands like that, just learn them, you'll use them so much it won't take long at all.
Hats off to anyone who's been typing on Colemak for longer than I have, I'm getting there :) At this point, I'm committed, and while I won't lie, it was really tough to change, it wasn't impossible at all and completely worth it! Thanks for reading!