This is a big usability improvement with very
little effort :-)

SCENARIO:
I have a "downloads" directory which contains many
files. Some are movies, some are pdf books, some
are mp3s.
I need to frequently sort the directory, mostly by
size or modified time.
Therefore I use list view, because it is the only
one that allows me to sort the items with one
click (and view the file size, but this is less
important). Well... in theory. :-)
The filenames in this directory are very long,
because I like to store the name of the author and
the actors/singers within the file name (in order
to do dynamic searches based on features). 

THE PROBLEM:
Since the filenames are very long, I don't see the
columns labeled "date" and "size", and I have to
scroll horizontally everytime I need to sort. This
is annoying. I can't really sort with one click.

POSSIBLE SOLUTIONS:

1. add a toolbar with four buttons, like longhorn.
These keys are labeled "sort by name", "sort by
date", etc. The big news is that these buttons
would always be visible, regardless of the file
name length. 
So you can REALLY sort with one click. 

As an added value, you would gain
one-click-sorting in icon-view mode too--
currently you can only sort via the menu.

2. word-wrap the file name in order to keep all
the columns visible. This is not always feasible
and silly since the previous solution is much better.