In order to profile some in house web application development and find out a couple bottlenecks that were appearing I went looking for a decent PHP profiler and found Xdebug. Because I am using the built in version of PHP on the Leopard Server, and a MacPorts version on Snow Leopard (we also have an application that fails miserably on PHP 5.3) it lead to some fun installing Xdebug on the Leopard machine since I didn’t want to reconfigure apache2 to use PHP 5.3 from MacPorts.
The crux of it is to grab the source of Xdebug, and then when configuring prefix your standard ./configure --enable-xdebug with the statement CFLAGS='-arch ppc64' or CFLAGS='-arch x86_64' as necessary. Compile xdebug as a 64-bit extension and it will actually work with a 64-bit version of Apache. With MacPorts it was as simple as enabling the xdebug variant and letting it recompile PHP.
I highly recommend using webgrind. It gave me more useful results than MacCallGrind, and didn’t require an hour hoping MacPorts could compile all the dependencies for kcachegrind (which would require graphviz as an additional install). Now I have some numbers to tell me where to look for proof old me is a moron.