How about creating a simple site where you simulate a horse race. i.e. give users part of the history data for horses, ask them to select the winners, and then reveal the true outcome. People would be betting for boast points.

A discussion board where people can discuss their heuristics for selecting winners would be great. For the famous horses, you can link to its Wikipedia page, Flickr photos, etc. if they exist to create a more immersive experience.

I, for one, would play with such a site for a while.