Wow.
On macosxhints.com there was an article posted with an link to a newly released pdf by the National Security Agency. The pdf is a detailed configuration guide for securing OS X (client). I thought I was a OS X hacker, but man,the NSA thougth of some things I never thought of. The pdf is very worthy to download and read, but the originating website is at least as informative.

Security Configuration Guides