There's a few options under the "Default Thread Subscription Mode" window. The 1st is "Do not subscribe" and 2nd one is "No email notification" (there's also instant, daily and weekly notifications). I'd figure choosing "no email notification" would keep you subscribed but without getting email.
You can check your current subscriptions with the "Subscribed Threads" -> "List Subscriptions" part. Under "Selected Threads" you can delete subscriptions to the threads you don't want to follow.
Unless you answer a lot of threads that you don't want to keep track of, that seems like it shouldn't be a problem.
Did that make sense? I'm not always sure if what I mean to say comes out correctly.