Here are the results from some distance field intersection experiments.
Inspired by slisesix by Inigo Quilez. A better explanation is on my reading list.
I also posted these on ompf. A single sample at 1024×768 takes about 6 seconds on a 2.4GHz Q6600 quad core CPU. Intersection works by stepping the field distance with a minimum step until the isosurface is intersected, and then the distance is refined with bisection method.