Apparently the Drupal team musta missed something in 5.4 'cause 5.5 was released almost immediately. The site is now running on 5.5.
While I was updating there was a notice the Subscriptions module got updated. It has changed a lot with many useful new features. You'll notice just below the content of a posting the word 'Subscribe'.. if you click on that a rectangle opens up with many options for subscribing to that post. Also in your 'My account' page you'll find a Subscriptions tab with many new options.