Navigating to parent directories in nautius could be a nightmare for new users.
 The parent-folders button was slagged in an Ars Technica review of Gnome 2.6:

"The last critical piece of understanding Nautilus' new behavior is the
parent-folders button. While moving into the tree structure is easy, at first,
it may not be clear to the user how to go back."

Refer to: http://arstechnica.com/reviews/004/software/gnome-2.6/gnome-2.6-2.html

This is a usability suggestion that I feel is very important.  It is important
because novice users will not read the manual to learn about the function of the 
parent-folders button, and may not try to right click on the background of the
window, which provides the option to browse back a directory.  So they might be
stuck not knowing how to back out of directories, as it's not obvious.

The "parent-folders" button in the lower left of each nautilus window does not
invite the user to click it.  The sunkenness of the parents-folder suggests it's
inactive, and just for informational purposes, kind of like the
Properties-related data right beside it, (in this screenshot, "151 items, Free
space: 64.3 GB") 

http://www.gnome.org/start/2.6/notes/figures/nautilus-parentfolders.png

Therefore I recommend:

-the parent-folders button should not be sunken.  Sunken implies inactive,
informational.  It lacks prominence, especially as it's at the bottom of the window.
-the parent-folders button should have a small, upward pointing arrow before or
after the directory name.  This would inform the user: "A useful menu will pop
out of me if you click me"
-the parent-folders button could have an icon right beside the directory name
that is a small folder picture with an arrow pointing right, then up, which is a
universally recognized symbol meaning "up a directory".  Or, the small folder
could have two dots on it, which is a universal UNIX symbol meaning "the parent
directory".

This ought to be quick and easy to fix.