I feel like this has probably been discussed before, but I couldn't find anything on the topic when doing a Super Search.
I'd like to see PM implement a "buddy list", so we can keep track of other users. There are certain people whose opinions and skills appeal to me, and I would like to keep track of their new posts. Having a list that I could add these people to would make that task a lot easier. There could be a feature where you can click a link to "show all new posts by your buddies" since the time of your last visit. I'm sure there are other ways a buddy list could be useful.