What happens to my blog when I graduate?
You can use the built in export feature to export your site to Wordpress.com or to other blogging services as well. See Exporting Your Blog for instructions. Keep in mind that you won’t have access to the same plugins and themes that are available at blogs.evergreen.edu.
Another alternative is to consider getting your own domain name and hosting your own Wordpress installation. Several web hosts provide pre-installed versions of Wordpress and make it pretty easy to get up and running. With your own Wordpress instance you would be able to install any plugin or theme you wanted. See: http://wordpress.org/hosting/ for a list of recommended hosts that provide easy Wordpress hosting.