The plugin uses the getImageData method on the Image object. It iterates over a portion of the pixels in an image, keeping track of color occurrences. It then returns the most dominant color and any other highly occurrent colors.
I was not anticipating on my little 3 hour jQuery plugin hitting the front page of HN, so I didn't take certain precautions. That's a good problem to have.
In any case, I've now moved the library to also be hosted on Github pages.
I have fall in love with Strava - minimal iOS running app (http://app.strava.com/mobile). I am not affiliated with them in any way.
I can also second Hal Higdon's site above.
A lot of people in a recent half marathon I ran were using the half marathon as a staging ground for their full marathon. By running a half marathon/5k/10k you can get a feel for what running an actual race feels like, which is invaluable.