Here is federal Chief Information Officer Vivek Kundra explaining data.gov and its many applications:
ReadWriteWeb had this to say:
New federal CIO Vivek Kundra is in charge of the site, which will act as a central repository for government data, including XML, CSV, KML files and more. At launch a mere 47 data sets are included and they appear to lean towards the least controversial matters. None the less, it's exciting to see the effort happening. Hopefully some awesome mashups are on the way!
But they also had very valid criticisms:
There are many, many sets of data available from the federal government but the Data.gov site says it was selective about quality and standards when choosing what to include. It's hard not to compare other sources of government data and feel disappointed, though. The privately built USGovXML.com contains far more data and was built by one independent developer over four months. That site lists ten Department of Interior XML feeds, for example, none of which appear on Data.gov. You can find a feed of food recalls there, but not on Data.gov. (Emphasis mine)
Getting at government information is a lot harder than it should be. Too many departments are hesitant to release anything that may make them look bad. Let's hope the institutional resistance to transparency will be changed or fade away.
Congratulations though to Kundra and his team for getting the site up and running in a (relatively) short amount of time. We need to make sure that data.gov remains active in its pursuit of bringing openness and transparency to the nation at-large.