Just to reiterate for those who got lost in the back-and-forth above. The code to insert below
<?php while (have_posts()) : the_post(); ?>
in the single.php page (or any page) and whether you use the default or custom permalinks should be…
<?php if(is_page()) : ?>
<a href="<?php bloginfo('url'); ?>/wp-print.php?page_id=<?=the_ID()?>">Print This Page</a>
<?php else : ?>
<a href="<?php bloginfo('url'); ?>/wp-print.php?p=<?=the_ID()?>">Print This Article</a>
<?php endif; ?>
For whatever reason, the plugin was not generating a print page for me (Not found error), but the above code fixed it. Apparently it doesn’t matter if you use permalinks or not to make the above work. No one’s going to want to link to a pretty permalink for the print version anyway.
Thanks to Gamerz and the above unnamed poster. This is a great plugin.