Google Sites has been updated to look more consistent with Google Docs, and added to the navigational menu, next to Gmail, Google Docs and Google Reader for easier navigation. Other changes: hierarchical navigation, sections are more customizable and there's a new "Pages" view that lists all pages, information about creator and number of revisions. "We switched the site settings area to use vertical navigation, to make room for some upcoming features like AdSense integration. We've also started to add some collaborator tools to the site management area. Less visibly, we made some major changes to our rendering infrastructure to improve performance and in preparation for new upcoming themes. This is meant to remain compatible with the layout customizations site owners have made, but it might have minor impacts on how your site looks."
More info: Google Apps Blog