This would be a great idea if implemented on the forum or a third party server. There are lots of knowledgeable members and many boards, this makes it difficult to keep up with everything that's posted over time. Having a system that notifies you when a user posts would be great. Extra points if you can choose the boards on which you would want to read their posts, for example, I might want to follow a user, but not want to be notified of their posts in Meta board.
This should be on forum, not using a third party tool,
It can be either. Third party tools have been useful in many areas of the forum.