Although the following was written with OS X v.10.5 in mind, it also works on Mac OS X and OS X Server versions 10.5.x and 10.6.x. Props where props are due: Dancing Engineer wrote the original piece, excerpted and lightly edited, below.
While logged into the server via SSH:
Change the user of the wordpress directory, whatever you’ve named it, and its contents to _www. Keep the group as staff, a group to which your user account belongs, and give write permissions to the group.
$ cd /Users/<username>/Sites/
$ sudo chown -R _www wordpress
$ sudo chmod -R g+w wordpress
With both of these methods, the WordPress directories have a permission level of 775 and files have a permission level of 664. No file or directory is world-writable.
To which, I can only add a hearty yippee!
