Those notifications annoyed me as well. I just go into the User CP and click "list subscriptions"
Now to disable those email notifications. Go into your User CP. Scroll down a ways and click on the "Edit Options" link on the left. Now Scroll down to the "Default Thread Subscription Mode" section and choose "No email notification" from the drop down menu.
Maybe you have already figured that out by now. For some reason it took me a long time to find that setting in the User CP... Brain fart that day I guess.