Vegard mentioned QuickTime Broadcaster in a blog entry yesterday. While QT broadcaster is certainly easy to set up and use, I have found it even easier to use some of the video broadcasting solutions in Max/MSP/Jitter. The jit.qt.broadcast object allows for QT streaming, but I have found the jit.broadcast object using RTSP to be somewhat more stable. Using Jitter also opens for all sorts of image manipulation, text overlays etc. as we are used to in the Max/MSP world.
Below is a snapshot from the help file of jit.broadcast. Getting started broadcasting video is as easy as clicking on a couple of buttons.