Original tutorial by Nick La, Web Designer Wall (read Responsive Column Layouts)
Resize your browser window to see the columns switch from 4 to 3, then to 2, and full width.
Try this one Nick, please! :)
No "!important", no clearing floats, no ":nth-of-type(4n+1)", no selectivizr.js needed :)
Works in IE like a dream! :)