Do your websites adapt to the device or screen on which they're being viewed? Do they accommodate viewing on a smart phone as elegantly as on a 1920-pixel wide monitor? Or a 5000px monitor? Or a netbook?
Responsive Design is the answer. It's a technique that employs flexible grids, fluid layouts, and most importantly - CSS3 media queries that let you change how things are laid out on the screen depending on the screen size (and many other factors), dynamically.