Notifications sound like a wonderful idea. Maybe when you'd be able to toggle the notifications in your settings, such as turning them on/off, using them for whisper notifications, friend notifications, or deciding to have sound on them or not. And maybe, when you double click someone, in the same area where you're able to click Whisper or Add to Group for a person, there's a Notifications check box as well. To alert you whenever said person types a post, even for a specific chat.
Could go far with this idea. Hopefully it'll be possible one day.