Just for the sake of me jotting this down somewhere…
Phi (the golden ratio) is approximately equal to 1.6180339887498948482.
phi is the decimal part of that: .6180339887498948482.
When laying out two column widths on a web page, using phi as the percentage of the wider column often provides a nice visual balance.
So, two columns would be set to width: 62% and width: 38%, which together add up to 100%, in order to approximate this ratio.
We’ve used this in the past on a few sites, including Wharton Center. I know we’ve used it to help layout others, but I just can’t think of any other sites right now.