Turning off the email alerts works for new threads, but not threads you are already "watch"ing. Once you are watching a thread, it's going to keep watching it as the email flag is set when you first post in a thread.
To unWATCH a thread, click on the Watched Threads link at the top of the page below the blue menu bar, then click the "Manage Watched Threads" drop down at the top right of the thread list.
You can disable "emails" only and still get in-site alerts (recommended) or you can disable all watched threads.