How to View User Subscriptions
From your dashboard, scroll down until you see the Users option on the left side of the screen. After you've clicked through to the Users screen, you'll see a list of all of the users on your site.
You can see which posts a user is subscribed to by editing a user. To do this, hover over a username, then click on Edit when it appears.
Near the bottom of the user profile screen you'll see the relevant subscription information. And yes, this does mean users can manage their own subscription preferences by editing their user profile. If you run a community site with a front-end profile plugin installed it's a nice feature to have.