The search history tab, for example, shows the last several queries performed from that Google account. Users can simply peruse the information, adjust their privacy settings or delete some of their stored data. Google hopes that by consolidating information relative to their services in a single place people will also rediscover accounts that they had forgotten about -- I for one just closed an Orkut account that was never used.
The new service should provide users with greater transparency and control over their data. However, while much of the concern about Google's data storage practices revolves around how and what exactly the company does to analyze and profit from user information, Dashboard offers little insight into that. More details on Google Dashboard can be found in a blog entry here.