Webgrind is also pretty easy to install. But, like the previous Xdebug post, some notes for future reference don’t hurt.
On Mac OS X 10.5, I had to change the $storageDir and $profilerDir to the following:
static $storageDir = '/var/tmp';
static $profilerDir = '/var/tmp';
because I did not have permission to write to the regular /tmp folder with my particular user. This step probably isn’t necessary for most people.