While looking for an easy way to access root UNIX directories in Finder, I have found following: Typing 'open /usr' in the terminal will open Finder window with the appropriate unix directory (in column view as a folder 'Private'). Also, typing 'open /private' will open a window with the root directories 'cores', 'Drivers', 'etc', 'tmp' and 'var'.
[Editor's note: You can also use the "Go -> Go to Folder" menu item and type the path to the folder to open a sub-folder; this doesn't seem to work (thanks sjonke!) for top-level folders.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2001060800012194