About Data.gov page states:
Data.gov is the world’s preeminent Open Data initiative. The purpose of Data.gov is to increase public access to high value, machine readable datasets generated by the Executive Branch of the United States Federal Government. Data.gov is a large-scale, distributed program involving the public, federal agencies, Open Data and civic developers, as well as several communities ranging from health, public policy and education to energy and technology. The data catalog website that put Open Data on the worldwide map, in May 2009, is undergoing a transformation into a cloud-based open data platform to deliver universal access to citizens, enablement for developers, and more effective collaboration options for government agencies.
Found some other fascinating websites.
Examples of what Cook County, IL is doing -- mapping data (mentioned in previous post) in some cases. But the integration of the data could be improved. For example, clicking on the # of violations issued does not categorize the information into types of violations, provide information on outcome or map them to a neighborhood. But it does provide a function where you can leave comments, contact the department/source of the data, or leave a comment to discuss the information.
The Cook County website is powered by Socrata.com Their page, "Maximizing the Utility of Your Data Assets" is amazing.