I think it would be really convenient to have a Facebook-like Alerts/Notifications page as a link on your profile page.
This would tell you things like:
- when someone comments on a thread/level after your comment
- when someone passes you on any of the leaderboards
Also maybe a Favorite Players/Friends list for your profile and you could receive notifications when your friends post new times and comments.
Maybe somebody else has thought of the Notifications idea?