Rob Allen has posted a full guide to his site today showing how to get Zend Server 6 up and running on an OSX installation:

I recently decided to upgrade my Mac's PHP to 5.4. One of the available options is Zend Server 6.1, Free edition. These are my notes how to set it up so that it works the way I develop.

He goes through each of the steps and includes configuration changes where appropriate:

• Installation
• Apache setup
• Zend Server admin configuration
• Command line control
• MySQL setup
• Apache vhost configuration
• Fixing sending email (doesn't work "out of the box")

He also points to the section of the Zend Server admin interface that shows the logs - error, access and a php-specific log.