personally, i would prefer if the query_posts returned no posts when the section_name value does not exist, although, i can understand the logic behind returning all posts as is the default.
is there a way i can test for a specific section_name value before i query_posts? if not, i would like to request this feature be added. something like:
<?php if( has_section_name('My_Section') ) : query_posts('section_name=My_Section'); ?> (the loop) <?php else: ?> (fail content) <?php endif; ?>