I've been helping do some profiling on a large Drupal site and the tool that I find indispensable for doing this is KCachegrind. Unfortunately, since I've migrated back to OSX on my main machine I've not had all the same tools that I rely on with Linux- specifically KCachegrind. However, since OSX is a *nix based operating system it is possible to get some of the same tools up and running despite it being a different platform. Using Fink, X11, and Xdebug, I've got KCachegrind running happily on OSX. I posted all the details of the installation on my blog. Hooray for open source tools working on different platforms!