Here's a list of applications and samples on the API:
A cross-platform remote desktop client and server written in python. Control a remote computer from a browser using Justin.tv.
Code: http://github.com/kvogt/jtvnc/tree/master
A dashboard widget for viewing Justin.tv channels OSX.
Code: http://github.com/justintv/jtv_dashboard/tree/master
Kim Bensen lost 211 pounds and uses Justin.tv live video to help others meet their weight loss goals.
Site: http://kimbensen.com/membership