Hi folks,
A few of us talked a bit on Tuesday (I think?) about managing CSS, and I mentioned that the new release of Zen does a very good job of organizing its CSS in a manageable way that can easily be overridden on a per-stylesheet basis.
For example, I'm currently developing the theme for our Drupal 6 site, which includes a theme for the public site and then a subtheme of it for our intranet site. I've overridden only the page-backgrounds.css and graphic-overrides.css files; the rest is inherited from our public site's theme (so I don't have to add new CSS in both places). This could be very useful for you if you create or manage multiple sites (for courses, for example).
Since the process of getting my sub-subtheme of my subtheme of zen working properly was a few hours short of intuitive, I wrote up a handbook page if you're interested. (I don't promise that it contains no errors.):
http://drupal.org/node/868732