Interesting, and handy for rapid prototyping, but I think Blueprintcss is the same idea, but much more flexible.

Great to see interesting reusable CSS reaching a maturity where such systems are now being developed.

I think another benefit of using a 960px grid is that coding your css widths and heights in em’s becomes easier. When you set the font-size in the body to 75% as a standard you can consider 1em as 12px in every browser.