It is the same with hand sketching, nothing beats fast mockup of what the end result could be.

Unless we can code faster than using photoshop. Untill that, photoshop will be around.

But that's what I see with generator like yeoman, bootstrap template and compass mixin, it's getting really fast to get a UI up and running. I mean making a quadratic color palette in sass is simple 3rd grade math, shading, grading and other color transformation are few mixin away. I can't have a function in photoshop that tell give me the best contrast on the font I use when I change the color of my button for example. And I am wondering how it has affected the workflow.

Exactly. You also get a much more unique look from PS.