Make the unix-type root directories visible in the Finder

From OS X Scientific Computing

Problem: /usr /bin /sbin /private are all invisible in the Finder

Apple hides the "scary" directories from its lusers. But there are often times you need to navigate to the /usr directory (or others).

Solution: Use the chflags command

Example:

sudo chflags nohidden /usr  

as a result, the /usr directory instantly appears in the root-level Finder window, save dialog box, etc.