Jakob Nielsen's Alertbox reports on their study of sitemaps, observing that among the sites they tested, sitemaps continue to be a useful tool to some people. While their study shows that they are rarely used, they can be simple, inexpensive tools to generate for the users who find value in the sense-making cues that a visual overview provides. Their recommendation is to continue to use them if you already produce them, but keep them static and don't add interactive effects to them.