I too have a wordpress blog. It's been great for me.
1. You find the subscriptions on the DASHBOARD and got to SITE STATS and look at the bottom.
2. Also on the DASHBOARD you go to USERS in the menu on the left (it's near the bottom). Click INVITES. That should get you what you need.
Thanks! I tried what you said and I now think the problem is that the people who have signed up didn't confirm their subscription when Wordpress would have sent them an email. I could see their email address but they are not fully registerd as users