One feature I wish was present is the ability to have multiple favourite lists.
I have a fair number of favourited questions, often for different reasons (e.g. questions I want to read later, others I want to try to answer later) and across different topics. It would be very nice if we could have multiple private favourite lists so I can find useful posts that I've saved for specific reasons quickly and easily.
I recognize that questions have tags, but I think we can agree that they do not have as much personalized utility as private lists.
My main inspiration is Amazon's ability to have multiple named wishlists, into which one can sort all of one's "favourited" items, even permitting duplication, which I find very helpful and pleasant to use.
Sorry if I missed another post asking this; I did try to look. (This one was somewhat related) :)