Alerting people when a forum post of theirs has been replied to would be nice. But I know what you're thinking, and yes, I know that would swamp people, so how about this:
When you are in the forums, how about having a button next to the reply button that's like a bookmark thing (even if it's not your post), and if you press that, it would alert you when someone has replied to that post. Pressing it again would turn the alerts off. It would make Forum Games run much smoother if you know when it's your turn. Also, no-one posts on my threads until ages after I've posted them, so it would be nice to know if they do.
EDIT: It could also be used on Storygames, so it will alert you when someone comments!