The 10.1.5 update of Mac OS X overwrote the PHP module for Apache, so if you’re already using Marc Liyanage’s precompiled PHP with Sablotron support, you’ll want to grab his new version. This new PHP also turns off a security hole, so check your scripts to make sure they’ll still run.
Note that if you’re using stock PHP, there’s no problem. But if you roll your own, or use Marc’s shared object module, then you’ll need to take action.