[Usability] Filechooser: Add/Remove buttons required?

[Daniel Borgmann <spark-mailinglists web de>]

Hello,

one thing I'm curious about is, whether there should be "Add" and
"Remove" buttons for the location list, like Federico is currently
using: http://primates.ximian.com/~federico/news-photos/gtkfilechooser-
2004-01-05.png
It seems to me like those are really difficult to place. On this
particular snapshot they don't break the layout, but it seems a little
bit awkward to have them as the very first items on the toolbar, even
before "Up". Most mockup suggestions seem to leave them out, which makes
those dialogs appear a lot cleaner.
So, are they needed as an alternative to drag and drop and context menu
items or could they be removed? Are the concerns accessibility related,
usability related or both?
I hope we can work out an answer to this, because I believe that it
would make it easier to design good possible layouts. 

Daniel