Consider the case of the Dutch national government: To provide convenient access to all governmental information citizens may need on a daily basis, it decided to bring information from 16 different ministries into one CMS.
To make centralization effective it needs to be paired with smart navigation. In larger contexts websites typically choose to provide more than one path to the same content. Technically this is achieved by tagging content instead of dropping it into fixed folders. Hippo CMS helps authors create these tags expediently and as of April 2010 citizens of the Netherlands have a number of centralized starting points to a large chunk of central government information (in Dutch):
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