I remember years ago when I had the revelation I was wasting time designing so much of the site in photoshop and that I could design much more usable and "organic" sites in HTML. I became adamantly HTML/CSS-first, using photoshop only for graphics.

These days I tend to do more of a mix, I like the expressive freedom of photoshop and the rigid grid structures and typography of HTML.

But I almost always start in photoshop after mocking. Probably from habit.