Problems with Rewriting the Slug for Taxonomies

I’ve been experimenting with custom taxonomies. The code seems to work for the most part, but the part to rewrite the slug isn’t working. Here is my code:

function build_taxonomies() {
	register_taxonomy('projects', 'post', array(
						'label' => __( 'Projects' ),
						'sort' => true,
						'args' => array( 'orderby' => 'term_order' ),
						'rewrite' => array( 'slug' => 'project' )
												)
	);
}
add_action('init', 'build_taxonomies');

Based on the Codex, it sounds like the rewrite slug part should make it so I can type “mydomain.com/?project=project_tag_goes_here”, but that doesn’t seem to work. Using plural form works fine: “…?projects=project_tag…”.

Note that I tried flushing the rewrite rules. I tried resaving my Permalink Settings and using $wp_rewrite->flush_rules() as described here:
http://codex.wordpress.org/Function_Reference/register_taxonomy