I can reproduce the crash on OSX.  After ~ 100 keystrokes, I get the following diagnostics:

Exception in Tkinter callback
Traceback (most recent call last):
  File "/Users/sasha/Work/python-svn/py3k-commit/Lib/tkinter/__init__.py", line 1399, in __call__
    return self.func(*args)
  File "/Users/sasha/Work/python-svn/py3k-commit/Lib/turtle.py", line 701, in eventfun
    fun()
  File "turtlecrash.py", line 12, in klt
    def klt(): seth(180); fd(vel)
  File "<string>", line 1, in seth
  File "/Users/sasha/Work/python-svn/py3k-commit/Lib/turtle.py", line 1936, in setheading
    self._rotate(angle)
  File "/Users/sasha/Work/python-svn/py3k-commit/Lib/turtle.py", line 3277, in _rotate
    self._update()
  File "/Users/sasha/Work/python-svn/py3k-commit/Lib/turtle.py", line 2660, in _update
    self._update_data()
  File "/Users/sasha/Work/python-svn/py3k-commit/Lib/turtle.py", line 2651, in _update_data
    self._pencolor, self._pensize)
  File "/Users/sasha/Work/python-svn/py3k-commit/Lib/turtle.py", line 545, in _drawline
    self.cv.coords(lineitem, *cl)
  File "<string>", line 1, in coords
RuntimeError: maximum recursion depth exceeded
Fatal Python error: Cannot recover from stack overflow.
Abort trap