Well, alot of times people reply to a topic and someone else quote them and they dont see it, so my idea is basically to have forum alerts and you will be alerted when someone:
Quote your post in a topic
Tag you in a topic(another suggestion, tag people in topic by doing @Name, could be helpfull for families and so on)
Also I noticed a forum bug that when we get a message we dont see it near "my messages", you need to view your messages to find out you got a message..