Love this concept. I love that this shifts your thinking away from specific widths and allows you to design from the content out.

I do agree with @barry above, the “fixed-width” nature of this is kind of a bummer. So… I made a few tiny changes to the codepen (see my fork here: http://codepen.io/bencallahan/full/mCwBe) so that it uses the fixed width column/gutter definitions to calculate the breakpoints but still uses percentages for the widths.

Good stuff @lesjames! Thanks for sharing.