I discovered a feature of this BB that you all may know about, but if not, it helps keep your cooky up to date.
I tend to read a lot of notes and stay on TFL for quite a while. During this time several new notes are usually posted by other TFL'ers. When you come back the next time, the new notes that you probably have already read will be flagged as new since your last visit. This is because the cooky is apparently set with your visit time at the start of the session. I have found that if you click on the graphic at the top left("The firing line ... enthusiasts"), this will update the cooky to the current date/time. You may have to click on it several times, since it seems to reflect your last several session times one at a time. For each click the "Your last visit ..." is updated. So that is the last action I take when leaving TFL.