I just ran into a similar problem–using the_tags() just didn’t show up.
I found that I was using the Loop example from the Codex. If I replaced it with the one in the default theme, the_tags() started working.
Originally, I had this:
if ( $posts ) : foreach ( $posts as $post ) : start_wp();
I replaced it with:
if (have_posts()) :
while (have_posts()) : the_post();
Of course, the bottom needed to be changed, as well, from an endeach to and endwhile.
Worked for me.