Don't use !important attribute. The CSS1 specification explicitly provides users the ability to override server-side style rules. This override, known as the !important attribute, is integral to CSS' ability to accommodate users' special requirements when rendering a page. A low-vision reader, for instance, might wish to specify an !important rule specifying a minimum font size for all documents.
By implication, server-side style sheets -- your style sheets -- should never attempt to use the !important attribute. If you ever find yourself tempted to "override the override," by using the !important attribute in your style sheets, remind yourself that the ultimate user override is always as close as that handy little [BACK] button.