I've been using this ReCSS bookmarklet for a long time now... it's one of the best tools I've found on the web. You drag-and-drop the bookmarket to your bookmarks toolbar, and when you need to force-reload the CSS on a page, just click on it and viola! No need to reload the entire page to see updated stylesheets.
Originally found on http://www.dojotoolkit.org/~david/recss.html.