One thing that's nice about the Mandelbrot set is that you can calculate each pixel independently of all the other pixels. This means if you have 8 CPUs, you can split the image into 8 parts and render it that way.

I apparently decided to try this out about 4 years ago. Here's the result: https://gist.github.com/jrockway/291074

Still slow. Need to run this on some machines at work :)