Why Learn Colemak?
Why would you go to all the trouble of learning a new keyboard layout if you are already proficient with another? It depends on your motives.
If you believe what you read on the net, and some of it should be taken with a grain of salt, then Qwerty was originally designed with the sole purpose of slowing down the typist so that typewriters would jam less and not need to be repaired as often. This does make sense and is very plausible considering the classic typewriter had arms that would jam or cross when the typist would type too fast thus slowing them down.
A response to this issue was the Dvorak layout. Dvorak is fast but one of its deficiencies is that the layout overly stresses certain weaker fingers. Colemak was designed to be easy to learn, balance typing between hands, and maintain recognised computer keyboard shortcuts such as Ctrl X, C and V to keep undo, cut and paste valid across layouts.
Basically Colemak is a VERY efficient keyboard layout compared to QWERTY and DVORAK. It has a good effort to output ratio whilst distributing the load evenly across the strongest fingers. The reason for this is