You can subscribe to a thread. Just above and to the right of the first post of a thread, you see a "Thread Tools" button. Click that and select from the drop down menu.
Then, it will show up on your "My Home" (button on the upper screen of TBN) if the thread is updated with a new response.
One thing I do, for older threads that may not get a response, is select the URL address and drag it to my desk top (with the TBN window reduced in size, but not minimized; left click, hold the mouse button down and drag it to your desk top). These are for threads I want to review...but again, are old enough that they may not get any more responses.