The text displayed by this confirmation dialog currently reads as follows:
"You are watching this thread. Use the button below if you would like to stop watching this thread."
The first sentence reminds the user that they are about to do something to a thread they have chosen to watch at some point, which is good. But the second sentence is little more than an explanation of how to use a confirmation dialog. (The fact that the button is labeled "Stop Watching" should be all the user needs.)
Perhaps it would be better if this space were used to make sure the user is aware of the results of this operation. I'd like to suggest that the above text be changed to something the following:
"You will no longer receive alerts or emails when this thread is updated. Are you sure you want to stop watching it?"
This should remind users that unwatching a thread will do more than just remove it from the "Watched Threads" page.