After reading the "Modern PHP workflow" article in the November 2008 edition of php|architect magazine which discussed unit testing (phpUnit), build tools (Phing) and continuous integration (Xinc), I'm inspired the learn more about some of the tooling available for PHP, especially Phing.
In the past I've often handled deployment to a production server by running the live site as a subversion working copy and simply running an "svn update" on the production box to deploy the latest version of the code.
Do you use build tools for PHP code? What advantages you you believe they offer over deploying direct from subversion? What should I look out for, or what gotchas might I face?