In my .emacs file I turn off global font lock:

  (global-font-lock-mode 0)

The effect is to turn syntax highlighting OFF in modes where there
would normally be syntax highlighting by default. The result in emacs
22.1.1 was to remove syntax highlighting from Perl, C, and Python
files.

In emacs 23.0.95.1 (build details below), this no longer works for
Python files. That is to say, various *.py files that I've tested have
syntax highlighting ON when I edit them in emacs with a normal
command:

  $ emacs example.py
  $ emacs api.py

Perl and C files have syntax highlighting OFF, on the other hand. When
editing one of the Python files, syntax highlighting can be turned OFF
by using the following procedure:

  M-x eval-expression <RET>
  (global-font-lock-mode 0) <RET>

In other words, by evaluating the expression from my .emacs file
manually. On repeating the expression, syntax highlighting remains
OFF, so it is apparently not acting as a toggle.

When I use emacs -q, syntax highlighting is ON by default when editing
any Perl, C, or Python file as expected. I've tried using different
positions for the global font lock line in my .emacs file, moving it
to the top, to the middle, and to the bottom, and that has no effect:
syntax highlighting is always ON in Python-Mode.

My full .emacs file is available here:

  http://inamidst.com/config/emacs

I'm using the following version of emacs from CVS:

  GNU Emacs 23.0.95.1 (i386-apple-darwin8.11.1, X toolkit) of 2009-06-20

Compiled with:

  $ ./configure --prefix=$PACKAGES/emacs \
     --with-jpeg=no --with-png=no --with-gif=no --with-tiff=no

And there doesn't appear to be any mention of this bug in
etc/PROBLEMS; I also asked in #emacs on freenode about this bug before
they advised me to file this bug by email.