The U.S. Department of Education just launched a new micro-site built on Drupal: teach.gov. At teach.gov you can learn what it's like to be a teacher and get the tools you need to launch your own career in education.
The site looks surprisingly crisp and modern for a government site, don't you think?
These kinds of micro-sites make a lot of sense. Visitors that are looking for particular information want instant gratification. It is much better to create a micro-site for this than to embed the same content two levels deep in ed.gov (also a Drupal site). No need to get bogged down with ed.gov's navigation, visual design or mix of target audiences.
While building highly targeted and compelling micro-sites makes a lot of sense, they can be expensive and time-consuming to build and maintain.