Was there ever a talk about pinsider tagging in a post? So if someone creates a topic that may be of interest to Robin, I can merely type @robin (or some variable instantiator) and robin would receive a notification of some sort. I don't think pinside mail or email is a good mechanism but maybe a bubble popup on login next to the username in the top toolbar with a list of posts you have been tagged in. Click on it and jump right to that post?
I can see this being used a lot. I could see its benefit in the marketplace. If I know "X" is looking for a game and it goes up for sale, tag X in the thread and they get notified to take a look.