When it comes to Fortress design, I am constantly plagued by an irrational need to live up to Moria, which means I have a large number of cavernous, pillared, non-square, monolithic rooms to make my fortress seem grand and awe-inspiring, often with one unassumiong entrance, and a lot of empty space to make the fort feels semi-deserted. As far as effiency goes, I mainly only consider how close the dining area is to the food stores, workshops to materials, depot to goods, and dorms to dining/meeting area. ANd even these rules are often gleefully broken if I find a neat way to connect a series of rooms. I tend to expand the size of my fortresses REEEEELLY slowly. I even disable invasions in the init file for the first five years or so, so that I don't need to worry about defenses (Defenses by far being my worst design skill). And as such, my dwarves have plenty of time to walk around. So it's mostly just art for me, I guess.
My current fort is much, much smaller than most I tend to build. This is because I took pains to make sure that I had all my rocks picked up and surfaces smoothed (And most engraved). I'm building it around a volcano in a tower/castle setup with four "Spiral" staircases with hallways between them. I suppose I should mention here that I am a HUGE fan of multiple z-levels. After all, how are you supposed to dig deep if you stay at sea-level?
I'll put up pictures of as soon as I figure out how the hell to get them saved right.