Mac OS X is BSD, while linux is gnu. The two are similar, but different. They also use different file systems:
Most often, its a human using a Mac, and a linux machine running services and managing networks. There are a few things that I need both linux and Macs to do for me:
I know there are many other ways to accomplish those goals, but I prefer to use tools that come standard on both platforms.
Alternative Security Options:
http://www.wasuvi.com/?page_id=2368
X11
http://forums.macosxhints.com/archive/index.php/t-57627.html
http://www.macosxhints.com/article.php?story=20030110062251974
Other cool Mac OS X and unix related stuff:
http://www.bigbold.com/snippets/posts/show/2745
Put unison settings in .unison, NOT Library/Application Support/Unison.
Beyond what I would do to make Mac more like linux:
These pages talk about installing more command line utils to make bsd more like linux.
http://www.emmes-world.de/mac-afp-homes.html
http://www1.gly.bris.ac.uk/~wookey/MEFTLG/index.htm
http://www.eecs.wsu.edu/~schneidj/mac-os-x-10.3.html