I wanted an easy way of hooking workrave up with other programs.
I figured being able to call an external script was the easiest way
of accomplishing this.

I have a patch for Linux/Unix-like systems (tested only on Linux unfortunately).
http://matt.wronka.org/stuff/projects/icpp/workrave/workrave-1.8.1-statechange_exec.patch
This patch causes workrave to look for and run the script
~/.workrave/statechange using '/bin/sh'.  The script gets passed
two arguments: the first argument is the new state, the second is the prior
state.

Thanks. Workrave now supports events through dbus:

obj = bus.get_object("org.workrave.Workrave", "/org/workrave/Workrave/Core")
workrave = dbus.Interface(obj, "org.workrave.CoreInterface")
workrave.connect_to_signal("MicrobreakChanged", microbreak_signal)

def microbreak_signal(self, progress):
  if progress == "prelude":
     print "Micro break warning"
  elif progress == "break":
     print "Micro break started"
  elif progress == "none":
     print "Micro break idle"
  else:
     print "Unknown progress for: %s" % progress