Index: wp-content/themes/twentytwelve/content.php
===================================================================
--- wp-content/themes/twentytwelve/content.php	(revision 22093)
+++ wp-content/themes/twentytwelve/content.php	(working copy)
@@ -36,7 +36,11 @@
 		</div><!-- .entry-summary -->
 		<?php else : ?>
 		<div class="entry-content">
+			<?php if ( has_excerpt() && ! is_singular() ) : // Display excerpt only if present ?>
+			<?php the_excerpt(); ?>
+			<?php else : ?>
 			<?php the_content( __( 'Continue reading <span class="meta-nav">&rarr;</span>', 'twentytwelve' ) ); ?>
+			<?php endif; ?>
 			<?php wp_link_pages( array( 'before' => '<div class="page-links">' . __( 'Pages:', 'twentytwelve' ), 'after' => '</div>' ) ); ?>
 		</div><!-- .entry-content -->
 		<?php endif; ?>