Stop building for devices and start building for the web.
The traditional web was like a newspaper. It had fixed dimensions, fixed columns, and it was never intended to fit in your palm. The modern web is like water. You put it in a cup, it becomes the cup; put it in a teapot, it becomes the teapot.
I especially thank Chris Coyier, Faruk Ateş, Paul Irish, Scott Jehl, and Brad Frost for their wonderful contributions to these slides and the modern web.