"Borrowed" from About.com
Standard dimensions for toe kicks are 3 inches deep and 3.5 inches tall. As the wee blurb at About.com states, you can go deeper and taller, but you really shouldn't go shallower and shorter.
Here in the land of cowboys and cowgirls wearing cowboy boots and cowgirl boots, (hopefully) respectfully, I wonder if them toe kicks needs to be deeper and taller, especially if those cowboots are pointy.
The bride's cowgirl boots. Mine are lost in storage...
And folks around these parts seem to have large, clown-like feet (the bride excluded). What's a dude concerned about toe kicks to do? Make 'em Texas sized!
The "public" kitchen area of our apartment building sports some Texas-sized toe kicks. They are 6 inches tall and a whopping 7 inches deep. You'd have to be a hell of cowboy to kick those toe kicks (and I would't want to see you in a pair of Speedos)!
As a side bonus [cough, cough], Texas-sized toe kicks work well aesthetically. If the toe kick is matched to the floor color (in this case stainless steel that approaches the color of concrete), light colored cabinets appear to float above the floor. Man, I bet that's relaxing to see after herding cattle (or cats) all day!
There's some architectural support for Texas-sized toe kicks: Robert Rasbach thinks toe kicks need to be 6 inches deep. And yes, he was a Texan.