I've been using Colemak for about 8 months and like it. A lot. Colemak just makes more sense than QWERTY. With Colemak, the keys you use the most are in the most convenient positions, for instance 'S' and 'T' are directly under your strongest fingers. Pretty smart. Having Backspace mapped to the Caps Lock key is an enormous benefit all by itself.
I've found that after the initial adjustment, I type much faster with Colemak and my fingers have to do awkward things a lot less. I plan to be typing for another 50+ years, so over that period I'll end up saving significant time as well as reducing strain on my hands.
But there is a down side. The biggest negative is the painful two weeks it takes to adjust. IMing at 1/3 your normal speed is annoying for everyone involved. So it takes a commitment to switch. The second negative is that it can be a little hard to go back and forth between Colemak and QWERTY. Not that hard, but you won't be as good in QWERTY. This means that when working on other peoples' computers, you might look a little clueless as you hunt and peck (until you explain that it's because you use Colemak, at which point you'll look like a genius). If you work on another period for any length of time, it's easy to install Colemak and just switch the layout.
I haven't used Dvorak, so it's hard to compare. But it makes sense that the closer to QWERTY you can get, the easier it will be to make the transition, and the easier it will be to switch back to QWERTY when needed. There are also some slight advantages to Colemak over Dvorak, the biggest being the remapping of Caps Lock.