I sometimes run into people on the Drupal IRC channels that have a theming issue they just can’t fathom – dysfunctional CSS. Some poor guy has overridden a core CSS class, but his styles just don’t work. I’ve been there myself before and I know it can be very frustrating.
With this, we have a form at admin/build/themes/settings/myTheme with a checkbox that allows us to enable all module css or disable all module css and a series of checkboxes that lets us selectively turn module css back on when all module css is disabled.