It is hard to compare American datasources with European ones, because of the different legal pre-conditions. In the USA all data produced with public resources such as taxes have to be available to the public without additional costs for usage. Most counties in the European Union (EU) follow an different strategy, where geospatial data have to be purchased. This is one point why for example the Inspire initiative and Data.gov can hardly be compared.
According to data.gov the platform was established with following reason:
The purpose of Data.gov is to increase public access to high value, machine readable datasets generated by the Executive Branch of the Federal Government. Although the initial launch of Data.gov provides a limited portion of the rich variety of Federal datasets presently available, we invite you to actively participate in shaping the future of Data.gov by suggesting additional datasets and site enhancements to provide seamless access and use of your Federal data. Visit today with us, but come back often. With your help, Data.gov will continue to grow and change in the weeks, months, and years ahead.
The platform provides different tools to search for data. One way is to use a searchable data catalog that includes access to raw data, but you can also use your applications to connect to this catalog. If in your opinion important datasets are missing you can suggest more datasets. The usage of the platfom is described in a tutorial.
RAW data is available in XML, KML, CSV/TXT, ESRI formats or as maps and others.
[via data.gov]
