I updated to OSX 10.9 "Mavericks" last night and pd-extended runs fine.

Only note is that a dialog box pops up when you first run it saying "You need X11 installed to run pd." In that case, simply download and install XQuartz which provides X11: http://xquartz.macosforge.org/landing/

I had XQuartz installed before but the OS upgrade must have removed it. In any case the dialog they give you includes some extra info so beginners should be able to figure it out.