I am running the svn version of matplotlib on a mac (OSX 10.6 with latest macports), and there is a problem with the output from demo_text_path.py. It does give the correct output on linux, so I assume the problem is either with the installed fonts on the mac, or with the mathtext code (in particular the tables in _mathtext_data.py). From the output, you can see that the text is correct in the upper subplot, but in the lower one, where is uses mathematical symbols, it is garbled. I get the same output for different backends (I have checked with macosx, GTKAgg and pdf).
If I can help to figure out the problem, please let me know,