Sometimes, I work really hard on a certain problem, but I don't manage to solve it. I want to request the ability to star it (or something similar) so the solution will be mailed to me when it's available. I know that I could check manually, but I often forget to do this. Also, having all solutions being mailed to me every week is not really an alternative, as I don't try to solve the problems every week. I hope this makes sense.
Edit: Also, it would be a great way to keep a list of problems you love! :)