A timely mashup reality check from John Montgomery.
Popfly, a mashup tool, depends on three things: data that is simple to access programmatically, interesting, and available under terms that enable users to work with it. As with most software endeavors, you can pick two.
The government has a huge amount of interesting data that's available under really great terms. Weather? Check out http://www.noaa.gov. Financial information? Start with http://www.sec.gov. Crime statistics? Dig around in http://www.usdoj.gov/. But how much of this is programmatically accessible? Very little, as it turns out.
Read the full post for examples and currently state-of-the-art work-arounds.