Start Backup allows you to force Time Machine to start without waiting for the hour frequency to pass. You can also do this by CONTROL-clicking on the Time Machine icon in the Dock and forcing Time Machine to start.
JOEL MUELLER It would be nice if this had some kind of response, like opening up the Time Machine preference panel to see that it has indeed started. Instead, version 0.1 does nothing but start the process (if your drive is hooked up). (Version 0.1)