I've been meaning to mention this for a while, but I've been somewhat overwhelmed with site-related activities of late (which is also why I'm again behind on the Pick of the Weeks)...if you're interested in learning Unix, we've actually got a pretty good teaching assistant over on the forum site.
Our moderator hayne has put together a Unix FAQ, which addresses many questions that newcomers will have, covering topics such as common commands, permissions, shell login scripts, and more. There's even stuff there that may be of interest to those with some Unix knowledge, including some information on scripting the shell directly and via AppleScript. There's also a collection of links to places where you can learn more about Unix.
While it's obviously not a comprehensive list of everything to know about Unix, it's a good starting point if you're wanting to learn more about this system that lurks beneath the aquafied covers of OS X.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060606070755996