in your settings/profile page scroll down until you see my settings -> my account -> general settings in the left hand panel
click on that link and scroll down util you see Messaging & Notification -> Default Thread Subscription Mode:
select either through my control panel only (this is useful if you want to see what updates have been made to threads you have posted in or created) or do not subscribe (only if you really do not want to know at all if someone has agreed or taken you to task - debating a point)