I didn’t know I had this problem till I stumbled on the answer. On checking though I found the my WordPress blog on my Powerbook just gave me an error.
After updating to Mac OS X 10.4.4, you may find that the connection between PHP and MySQL running on your local webserver is broken.
The solutions in that macosxhints article ‘Repair PHP/MySQL connections in 10.4.4’ fixed it.
I followed the instructions at the Apple Knowledgebase article but they didn’t work. I also needed the information from this comment at macosxhints (link above):
… keep in mind, for Client, you have to turn around the settings, so either
socket=/var/mysql/mysql.sock in my.cnf, or
mysql.default_socket = /tmp/mysql.sock in php.ini.
Now all is well again.