Theres a bug with the latest vanilla version of pd in OS X (at least 10.7, don't know about older versions) that causes pd to crash when trying to reopen patches from the last session.  It is filed here:

https://sourceforge.net/tracker/index.php?func=detail&aid=3396316&group_id=55736&atid=478070

As a work around, I'm looking for a way to clear the list of patches to reopen, but I can't find where they are stored.  Does anyone know?

Cheers,
Rich