I had been on Dvorak for 15 months before I switched to Colemak. My main reason for switching was that the Ctrl+C and Ctrl+V keys in Dvorak were really REALLY getting on my nerves. Half the time I was using Ctrl/Shfit+Insert, and then half the apps I was using weren't supporting these keys.
In my job(web development) I actually have to copy+paste a lot, so any benefit I saw from Dvorak was extinguished by not being able to copy text with my right hand on the mouse and left on the keyboard shortcuts.
For general ergonomics, Dvorak felt a bit more comfortable, but Colemak is the most productive layout I've dealt with so I intend to stay with it. Speedwise, I type 80WPM on all 3 layouts, so comfort and convenience are the deciding factors.