Although I stand by my criticism of IDLE not offering the option of
switching off cursor blink, I've now discovered that the problem was
with Fedora 10 no longer executing xrdb .Xdefaults; once I added that
line to my .bash_profile the cursor blinking stopped.

However, that is no help to people using Windows for whom the only
solution is to manually edit the EditorWindow.py file every time they
install a new version of Python.