I upgraded Mac Os X to the version 10.6.1 and I found that my mysql database stopped working, This is how I fix it:
Open a Terminal and type
sudo ln -s /usr/local/mysql-5.0.51b-osx10.5-x86/* /usr/local/mysql
Then, look for the MySQL icon in the System Preference panel and click it. Let it reopen (as the message says), and that’s it. Mysql is running as it was before upgrading the operative system.
Hope it helps.