The government has created an official URL shortener, Go.USA.gov. You have to be be a government employee to use it. As of about ten minutes ago, "Go.USA.gov has shortened 252 URLs that have been clicked 16129 times". Only "gov, .mil, or .si.edu URLs" links can be shortened by those that have access. You can see it is not really popular, but it is also new. The thinking is likely that such 'official' government shortened URL links will be much more trusted then even others, even those that have forms of spam and phishing protection.
More at http://www.techcrunch.com/2009/10/13/go-usa-gov-our-taxpayer-money-hard-at-work-shortening-urls.