It is nice to have so many ways of filtering and sorting the thousands of threads in MO. So there I go, and my list of favorites becomes longer and longer. Most often I obviously add rather recent threads, but sometimes old ones. I can of course sort them by date, but it would be helpful to have the additional possibility of sorting them by the date when I added them. Some old topics may become "obsolete" for me (how can such a thing exist in mathematics? obsolete? well you guess what I mean), while others contain useful references or (why not) questions for further research "some day when I'll have time" - or they are just so beautiful that I want to keep them 'forever'.
At a time when I was very active on Mathlinks, I used to keep my own text file with links to the most interesting ones of my numerous favorites, naturally in the order I encountered them. But thus they are not nicely displayed as a list.
In a web browser, there is the possibility of creating subfolders in the 'favorites' folder. I would not ask for such a feature in MO and the associated sites, but knowing that the internet has such a good memory, I guess that the information about when a user has added a favorite is kept somewhere, similarly to the "edit history", and even if not: why not implement that from now on? It should not be complicated to make such an option available as another tab.
Of course, that should only concern one's own favorites. Even though it is often interesting (as many of you will certainly confirm) to look at the favorites of other users, I would not want to become a "big brother" to somebody else by looking up when he as added a certain one of his favorites.