After a meeting with the government of Australia, Dries asked if there still are goverments not using Drupal. Indeed a majority of governments is using Drupal now for one or more of their websites (120 out of the 200 UN member states).
Complete list of governments that are using Drupal are Albania, Algeria, Andorra, Argentina, Armenia, Australia, Austria, Azerbaijan, Bangladesh, Barbados, Belarus, Belgium, Bermuda, Bolivia, Bosnia and Herzegovina, Botswana, Brazil, Bhutan, Burundi, Cambodia, Canada, Cayman Islands, Chile, China, Colombia, Costa Rica, Croatia, Cuba, Cyprus, Czech Republic, Denmark, Dominica, Dominican Republic, Ecuador, El Salvador, Egypt, Estonia, Ethiopia, Finland, France, Gambia, Germany, Ghana, Greece, Guatemala, Guyana, Honduras, Hungary, India, Indonesia, Iran, Iraq, Ireland, Israel, Italy, Jamaica, Japan, Jordan, Kazakhstan, Kenya, St Kitts-Nevis, Kuwait, Kyrgyzstan, Laos, Latvia, Lebanon, Lithuania, St Lucia, Luxembourg, Macedonia, Malaysia, Maldives, Mexico, Moldova, Mongolia, Nepal, the Netherlands, New Zealand, Nicaragua, Nigeria, Norway, Palestina, Panama, Paraguay, Peru, Philippines, Poland, Portugal, Romania, Russian Federation, Rwanda, Saudi Arabia, Serbia, Slovakia, Solomon Islands, South Africa, Spain, Sri Lanka, Sudan, Syria, Taiwan, Tajikistan, Tanzania, Thailand, Timor-Leste, Tonga, Tunisia, Trinidad and Tobago, Turkey, Turkmenistan, Uganda, Ukraine, United Arab Emirates, United Kingdom, USA, Uzbekistan, Venezuela, Vietnam, Yemen and Zambia.
However, there are some governments not using Drupal, at least that we are aware of. Most of them microstates, or (internet) restricted states. There are four countries I had expect to use Drupal: Iceland, Bulgaria, Switzerland and Sweden. But I guess that will change soon.
Other countries not yet using Drupal include Afghanistan, Angola, Antigua and Barbuda, Bahama's, Bahrain, Belize, Brunei, Burma, Burkina Faso, Burundi, Cameroon, Cape Verde, Chad, Comoros, Congo, Côte d'Ivoire, Equatorial Guinea, Eritrea, Fiji, Gabon, Georgia, Grenada, Guinea, Guinea-Bissau, Haiti, Kiribati, North-Korea, South-Korea, Lesotho, Liberia, Libya, Liechtenstein, Madagascar, Malawi, Marshall Islands, Mali, Malta, Mauritania, Mauritius, Micronesia, Monaco, Morocco, Mozambique, Namibia, Nauru, Niger, Oman, Pakistan, Palau, Papua New Guinea, Qatar, Samoa, San Marino, Senegal, Seychelles, Sierra Leone, Singapore, Somalia, Suriname, Swaziland, Togo, Tuvalu, Uruguay, Vanuatu, Vatican and Zimbabwe.
If you happen to be a citizen of one of these countries and know a governmental site using Drupal, please add this to the list: http://groups.drupal.org/government-sites