In response to those seeking clarity on the subscribed thread notification emails, I now understand what you are referring to.
Over the weekend a change was made to possibly fix an issue some members are having with subsequent replies to threads they are watching. As you will note if you have received a "watched thread" notification, at the bottom there is text that states "you will not receive any further emails about this thread until you have read the new messages" linked to from that email. We have found that users receiving a preview of the text in the thread opt not to login and view the thread, resulting in no more email notifications. An increasing number of support requests about broken email notifications have resulted.
If you received an email notification for a thread now, you will no longer see a preview of the content. However, you will be more likely to click through to the content and this should enable further email notifications. It is important to remember though, if you are not logged-in when clicking through, the system will not know that you have caught up on the new content.