If you don't want to wait for MS....there are some tools on the market, that allows to implement MULTIPLE taxonomies for your SharePoint portal (WSS/MOSS), so you don't rely too much on main navigation: SharePartXXL offers an extension with cross-site centrally managed, tree-style categories that can be used in all lists and libraries to categorize the content using different taxonomies, e.g. organizational, by products or geographically. Metadata from categorized content can be shown in dynamic category-based sites for navigation, related items are shown in the items detail view resulting in some kind of browsable corporate knowledge network. Please check it out: http://www.sharepartxxl.com/products/taxonomy/default.aspx